Because TV involves unionized people, and unionized people sometimes go on strike. When the Writer's Guild of America (WGA) goes on strike, this largely shuts down the Hollywood process, since writers are needed for script rewrites on set and
actors Teamsters aren't keen to cross picket lines (in fact, they have it in their contract that they're immune to punishment should they honor any picket line). Strikes come as a result of bargaining falling apart with management, as represented by the AMPTP.
Strikes affect movies too, but the effects are a lot easier to notice for TV.
Disney Animators' Strike of 1941
In 1941, Disney's animators joined the Screen Cartoonists' Guild and went on strike on May 29 for the profit promised from Snow White (which many animators took unpaid overtime to complete) and in response to the firing of prominent lead animator Art Babbitt for joining the Guild. Six weeks later, a federal mediator found in favor of the Guild, and "The Mouse Factory" has been a union joint ever since.
Rumor has it that the nasty, drunken clowns from Dumbo, released in 1941, who decide to "hit the big boss for a raise" are a Take That at the striking animators.
1960 WGA / SAG Strike
January 16 - June 10. The writers got the studios to pay into the WGA health and pension funds. Film writers got bigger residuals, and television writers got their wages doubled.
1978 Animation Guild Strike
Went on strike over runaway production (studios started outsourcing animation to lower-wage countries). Led to a new clause where studios had to employ a certain number of employees before they could subcontract. The Guild lost this protection in the 1983 strike (see entry below).
1980 Hollywood Actors' Strike
Most notable for the fact that the previous season, Dallas had aired its famous "Who shot J.R.?" season-ending cliffhanger, and the strike meant viewers had to wait five months rather than three to find out who the shooter had been. Extra strong measures were taken to prevent the solution from leaking, including filming shots of just about every member of the cast and crew, including J.R. himself, pulling the trigger.
1983 Animation Guild Strike
Lasted 10 weeks. Again, the Guild fought over the runaway clause (see 1978). They lost because, well, the studios subcontracted to overseas studios and also to companies in other counties and states (and thus outside of the Guild's jurisdiction).
The final nail in the coffin was on the 9th week, when Disney animators decided to take the "financial core" status  and return to work. The Guild lost all hope and called off the strike, losing the "runaway" clause in the process.
1985 WGA Strike
A two-week strike that ended badly for the unions, forcing them to take a crappy residual (read royalty) on VHS sales, a low number that has had far reaching effects with the advent of DVD and downloads.
1987 Directors' Strike
This strike only lasted three hours and five minutes.
1988 WGA Strike
This one is the WGA's longest strike (March 7 - August 8), over reduced residuals for hourlong series and foreign reruns.
- The biggest event resulting from this strike might be the beginning of the end of the Soap Opera in the U.S. When this happened, soaps were left without their most experienced writers, and the quality of the shows nosedived and never recovered. Six years after the end of the strike--while the soaps were still recovering--came the OJ Simpson murder trial, which left the soaps completely off the air for weeks. Soaps, which were originally ratings juggernauts, never really recovered. In The New Tens most of these shows (with decades-long runs) face the risk of being, or have been, cancelled.
- The ends of Moonlighting and Kate & Allie are attributed to the strike.
- The second season of Star Trek: The Next Generation got through the strike by using a Clip Show and some previously-written scripts for the abandoned 1970s Star Trek: Phase II series.
- Star Trek V: The Final Frontier, meanwhile, was forced to go into production with an unfinished script. It shows.
- FOX bought COPS, being a reality show that did not require writers (but see above), and it became a very successful long-running show.
- Small Wonder had an episode about a strike at Ted's company.
- CBS reran non-holiday-related Peanuts animated specials to help plug up holes in prime time -- to the point that TV Guide pointed the tactic out in a highlights listing.
- The Simpsons gave a shoutout to this strike in Last Exit to Springfield where Homer and the Nuclear techs recall the Springfield strike of '88.
- A Bloom County Sunday strip acknowledged the strike. It ran an old strip presumably rewritten by a scab writer, with the new dialogue being anti-union.
- Michael G. Wilson had to finish the script for Licence to Kill as the strike precluded Richard Maibaum from working on it. It shows.
2007-8 WGA Strike
In 2007, unhappy over low royalties for DVDs, and low or no residuals for Internet distribution of shows and for Internet-only broadcasts, the WGA went on strike from November 12, 2007 to February 5, 2008. The strike was concluded with a deal that granted or increased some Internet residuals, while not affecting DVDs.
The strike was also the first of its kind to take place in the era of the internet. As a result, writers had a more direct line of communication with fans/the general public, which led to unprecedented public support. When Joss Whedon announced a "meet Joss Whedon" day on the picket lines, fans streamed in from as far away as Australia.
The results of the strike:
- 24, with only eight episodes in the can before the strike, decided that an incomplete season would not be a good thing and delayed Season 7 until January 2009. A two-hour Made for TV Movie prequel aired November 2008.
- This also meant that Kiefer Sutherland, who pleaded no contest to his second DUI charge, got to serve his 48-day jail sentence in one go. He'd planned to do it in two bits, during the production gaps.
- Thirty Rock is an interesting case since the series is about the production of a Show Within a Show and several of the regular characters (including the protagonist) are writers. According to Word of God, the strike didn't happen in the 30 Rock universe.
- Bionic Woman got eight episodes done, but was then axed during it.
- Journeyman had all its 13 episodes written before the strike, and was cancelled for low ratings; the strike is probably responsible for all 13 episodes actually making it to air rather than being DVD-only.
- CSI had a 24-episode run cut to 17 and CSI New York to 21.
- For UK viewers, this resulted in a) sudden gaps of a couple of weeks to avoid catching up on the first and third (CSI: Miami airs after the other two) and b) the situation where UK viewers ended up mere days behind their US counterparts, resulting in Preview Tapes Not Available being stated because the actual episodes had yet to even air when the Radio Times went to press.
- Smallville from 24 to 20, with the last five episodes incomprehensible. Well, more incomprehensible.
- South Park carried on and bashed the strike in one episode, in which the World Canadian Bureau (WGA) encourages Canadians to strike for "more money". Many animated programs, including South Park, were written under a different union than the WGA.
- IATSE covers the writers on most animated series. This is a point of contention between the WGA and IATSE.
- The ironic part of the episode was Kyle's episode-ending speech about how people shouldn't strive to get money from unproven revenue sources -- in the case of the episode, online content. That summer, Parker and Stone had inked a deal to stream South Park episodes on-line, with ad content, that was estimated to bring them $75 million over the next four year. So it's either Hypocritical Humor, or just plain hypocrisy. Your choice.
- The stupid part is that DVD's are very proven ways you can get money and people working on the internet can make a living.
- Family Guy was one of the hardest-hit series during the strike, resulting in two episodes being screened without Seth McFarlane's permission, the sixth season ending with only 12 episodes, and the entirety of the seventh season consisting of episodes held-over from the sixth season. American Dad went a little better, with the third season consisting of 16 episodes.
- Heroes' second season was also cut from 24 episodes to 11 (that's more than half a season's worth of episodes), with the final episode of what was supposed to be the first arc hastily altered to wrap up the season. The planned spinoff Heroes: Origins was never produced. The idea that Volume 2 went "slow" (when it was being planned out for a 24 episode season) likely resulted in the rapid pacing and constant plot shifts of Volume 3.
- The fourth season of Lost was supposed to have 16 episodes, all aired in a row. The strike cut it down to 13 episodes, with a month-long break between episodes 8 and 9.
- Angels & Demons was delayed by a few months.
- ER and Scrubs, both scheduled to end during the 2007-8 season, were extended one more season to have a proper sendoff (with Scrubs channel-hopping to ABC to do it.)
- Supernatural had its normal 22 episodes cut down to sixteen, with the last few episodes time-jumping through how much time Dean had left.
- A few shows got lucky. The strike almost exactly coincided with the time the writers of Burn Notice were supposed to be taking a break anyway, and USA actually ordered more episodes for Season 2 than had been planned pre-strike.
- The Stargate Verse was unaffected: Stargate Atlantis is produced in Canada and had wrapped filming before the strike started anyway.
- The late-night talk shows went on hiatus for the first couple of months, but returned in January rather than lay off the non-striking production staff. Notably, David Letterman negotiated a special deal with the WGA to let his show and Craig Ferguson's return with their full writing staff; the others (including The Tonight Show, The Daily Show, and The Colbert Report) relied on non-scripted material for the duration of the strike.
- The Sarah Connor Chronicles ended abruptly without really ending the season; on the other hand, since it was used as a midseason replacement, the absence of competitors may have helped it gain an audience. It was renewed for another season.
- Joss Whedon got bored and wrote Doctor Horrible's Sing-Along Blog. Dollhouse had its development put on hold as a result.
- Brothers and Sisters went through a couple of large time-jumps plot-wise.
- A lack of a Warner Bros. summer blockbuster for 2009 meant Harry Potter and the Half-Blood Prince was moved back to fill that slot (The Dark Knight did so well that they weren't worried about having a successful '08 without it), and Twilight moved up a month to fill its slot. The announcement that Harry Potter was being moved came after the TimeWarner-owned magazine Entertainment Weekly gave that film the cover of its Fall Preview issue, leaving EW with egg on its face.
- Pushing Daisies was a clear casualty--the strike hit nine episodes into its first season, and ABC decided not to bring it back in the spring (like every other show brought back after the strike). Waiting until the next TV season resulted in it being off the air for almost a year, and proved to have sapped its audience beyond recovery.
- Some shows that were to air over the summer were rushed out a few months early to compensate for the strike. Hells Kitchen was aired in April instead of June.
- The re-imagined Battlestar Galactica Reimagined was halted mid-season, and Earth, which was supposedly to be shown in the next to last episode, ended up appearing in the midseason finale.
- In addition, because the writers knew that the show would end at that point if the strike went south, Sometimes a Great Notion was written in a way to resemble something of a series finale. An understandable effort that ended up undermining the show as a whole when the strike ended and the series went on, forcing the writers to restart and end the story in the space of 11 episodes. This resulted with the "show-ending arcs" (Fleet slowly dying out, the Cylon Civil War etc...) being squeezed to the point of unrecognition and was the source of some of the more controversial elements of the last 11 episodes.
- Bones' third season was cut to 15 episodes, and the season long serial killer Story Arc was given a problematic ending.
- The script for Transformers: Revenge of the Fallen was supposedly worked on by Michael Bay while Roberto Orci and Alex Kurtzman were on strike.
- The script for Quantum of Solace was finished two hours before the strike commenced and some filming took place with Daniel Craig having to work on the script with the director. It showed (NSFW language).
- Greek's first season was halted after 10 episodes. These episodes were then compiled as "Chapter One", and the rest of the season as "Chapter Two". Because of this, the later seasons were also divided into chapters.
- Las Vegas was cancelled on a Cliff Hanger that was never even intended as a season ender.
- Because Britain and Australia (and presumably other countries as well) ended up with less American content than they were expecting, some channels relaunched old shows, leading to a new season of both local versions of Gladiators and the still-running reboot of Good News Week.
- When the writers for Power Rangers went on strike, Disney went ahead and hired scab writers to finish most of Power Rangers Jungle Fury with the WGA writers returning with four episodes remaining to write. It actually worked out fairly well as Jungle Fury is (at least) seen as a step back in the right direction after years of declining quality.
- Eastbound and Down had only just finished work on its pilot episode when the strike hit, meaning the rest of the first season wasn't made until late 2008 and the show itself didn't air until early 2009. The effect of this hiatus is only really noticeable in the changed appearances of Dustin's kids, though, since their actors had obviously grown more in the year off.
- Attributed to the cancellation of Just Jordan, due to it being the only Nickelodeon original show at the time to feature WGA writers.
1968 ITV Strike
A franchise shake-up led to a lot of workers being forced to move location (there were no actual job losses). A dispute over who would get redundancy payments (specifically over those moving company, but not location) led to wildcat strikes and lock-outs.
A month later, the strike ended, all sides claiming victory. The bitterness would continue, though...
1979 ITV Strike
Electricians (an important job in TV production) at Thames Television, the station who provided the ITV service for viewers in London Town from Monday to Friday afternoon and undoubtedly the Team Mom of the ITV network, walked out over a pay increase they felt was derisory. The management tried to maintain a normal service, but other workers refused to help do this. Thames told the strikers to "return or else".
In response, ACTT (the broadcasting union) got 13 of the other ITV regional stations to go on strike as well, this being a time when sympathy strikes were still permitted in Britain. Channel Television, serving the Channel Islands, was the only company in the network to continue broadcasting during the blackout, because the tiny size of its audience meant a loss of revenue could have put it out of business.
The result was the nearly total shut down of ITV for ten weeks (10 August to 5.38pm on 24 October) and the loss of around £100m in revenue for the striking companies. Channel Television sustained itself with extended regional news bulletins and Western movies.
In other areas of the UK, with only three channels at this point in time, The BBC was the sole alternative, resulting in Doctor Who getting its highest ratings ever for "City of Death", a record that even David Tennant's regeneration barely scraped.
- Doctor Who did not escape strike action. That season saw "Shada" ultimately cancelled after strike action prevented the second and third studio session from taking place, although in that case it was a tube strike, not an industry one. The story was eventually done as an audio drama for the 8th Doctor in 2003.
- This period had "work-to-rule" going on a fair bit. The DVD for The Hitchhikers Guide to The Galaxy includes an extra showing the cast and crew trying (and just succeeding) to get a scene filmed before the lights were turned off.
The strike ended in a victory for the unions. ITV wasn't able to air much newly-produced programming for two-and-a-half months (showing lots of episodes of 3-2-1 instead), but gradually recovered its audience.
It was the longest dispute in British television history.
- Also known as "fi-core". It's a legal category where you only have to pay reduced union fees that only covers your union contract and benefits. You cannot participate in union activities, but in return you don't have to obey the union's regulations, can work at non-union companies, and, most importantly, you can continue to work during the strike.