Band of Brothels

This is an organization that supervises, um, you know. Working girls. Ladies of the night. Women of negotiable affection. Those in the oldest profession. Those who turn tricks for goods and/or money. They who walk certain streets. Soiled Doves. Women who follow camps. Girls who are on call. Courtesans. In groups: A Tray of Tarts, a Blazon of Strumpets, an Anthology of Pros. Or pick another euphemism. In other words: Prostitutes.

Certainly a Weird Trade Union. Sometimes the Hooker with a Heart of Gold will be a member.

Anime and Manga

 * Casca from Berserk was taken in the protection of a band of prostitutes in a refugee camp when she wandered away from the protection of the elf cave that Guts left her in. So protective are they of the wayward, insane girl that they bandaged Casca up as a syphilis victim in order to keep the lecherous eyes of men off of her, as they did not force her into prostitution due to her condition. The girls are led by Luca, one of the few genuinely nice characters in the Berserkverse, who acts much more as a mother figure rather than a madame, splitting her shares evenly among the other girls and coming to their aid in the most dangerous of situations.
 * In Is It Wrong to Try to Pick Up Girls in a Dungeon?, Orario's Red Light District has accrued around - and is run by - the temple to Ishtar, where there's very little differentiation made between sacred prostitution and the other sort.

Comic Books

 * The prostitutes of Old Town in Sin City, who've banded together into an army to keep the police and pimps out of the district.
 * In the Buck Godot: Zap Gun for Hire stories by Phil Foglio, Buck's friend Louisa dem Five runs a brothel, the Velvet Fist—and has established, as of the "Gallimaufry" arc, a Velvet Fist franchise on the title Space Station.

Fan Works

 * In The Basalt City Chronicles, the Order of the Courtesan (basically a "saint" in the Smilodon religion) oversees baths and brothels. This creates some In-Universe Values Dissonance, as in Furriston brothels are illegal due to their tragic history.

Film

 * In Unforgiven two cowboys badly injure a working girl. Her fellow ladies of the night pool their resources and put a bounty on the heads of the wrongdoers. Clint Eastwood's particular brand of badassery ensues.
 * Deuce Bigalow II has the European Association of Gigolos.
 * Not a technical organization, but Lady Eboshi's headquarters in Irontown is staffed largely by ex-prostitutes.
 * The Taiwanese art-house movie Flowers of Shanghai is about the lives of Chinese "Flowers" (i.e. high-class prostitutes) in 19th-century Shanghai. The whole movie takes place within the confines of the houses of pleasure, without a single outdoors shot.
 * Live Nude Girls Unite! The women at a San Francisco strip joint unionize. Documentary.

Literature

 * Kushiel's Legacy by Jacqueline Carey: Prostitution is a sacred profession; there is no shame in it whatsoever, and the prostitutes (male and female) are all erudite and intelligent. There is a system of houses, each named after a flower and specializing in an...aspect of sexuality (though, in this world, alternative couples are common); for example, Valerian specializes in prostitutes who like pain, to put it delicately, and Cereus house is famed for its particularly erudite (verbally and sexually) servants.
 * Wait...how can you be sexually erudite?
 * It's amazing what some people can do with a labial-palatal consonant.
 * Or consecutive vowels.
 * For a bit of clarification, the Court of Night Blooming Flowers is the collective for the oldest and most prestigious brothels in the capital. There is a larger guild as well that provides assistance and sets regulations for the less prestigious establishments and independents.
 * In Discworld, there's the Seamstresses' Guild. "Hem Hem." Let's just say that they don't sew a lot.
 * Except that, in Night Watch, we find out that some of them do.
 * The latter are called needlewomen and present for convenience's sake, there to cater to the kind of people who make the mistake of going to a "massage parlour" for an actual massage.
 * Seattle in the 1800s used the same term. Their motto was "A stitch in time will cost you a dime. All night alterations for a dollar."
 * Makes some sense, given that in those days sewing was an acceptable form of self-employment for women, so many women who actually engaged in less legitimate activities would put that on any legal forms as their job.
 * Robert A. Heinlein novel Friday. The California Confederacy has a hooker's union, which sponsored legislation to have the government train and license women who wanted to be prostitutes, then pay them a subsidy not to sell themselves. The union did this to reduce the total number of prostitutes so they could keep the union scale high and make more money themselves.
 * The creation of an association of this kind is the main plot in Mario Vargas Llosa's novel Pantaleon y las Visitadoras (known in English as "Captain Pantoja and the Special Service").
 * The city of Camorr in the Gentleman Bastard Sequence series by Scott Lynch had two such organizations dividing up areas of the city. It's revealed they fought a very long and bloody gang war to take control and form a monopoly, so much so that when Magnificent Bastard Capa Vencarlo Barsavi took over the entire city's criminal underworld, over a hundred gangs all told, he choose to enter into a partnership with them in exchange for their nominal fealty to him rather than enforce subservience to the extent he does on the rest of the city.
 * Islands in the Net by Bruce Sterling has The Church of Ishtar along these lines.
 * Vorkosigan Saga's Beta Colony has its LPSTs: Licensed Professional Sexual Therapists. The hermaphrodite ones are especially popular.
 * Spider Robinson's Callahan's Lady series is about a bar/brothel run by Lady Sally, wife of Mike Callahan. The working girls have generous benefits, are well taken care of, and the sex is consensual and mutually supportive.
 * The Cult of Ashera mentioned in Neal Stephenson's Snow Crash, which used cult prostitutes to spread their metavirus.

Live Action TV

 * The Guild of Companions in Firefly, although Companions are more like Ancient Greek Hetairai, or a cross between prostitutes, geishas, therapists, and confessors.
 * Nandi's brothel is rather bizarre, because while on one hand it's a standard brothel run by a madam, it's also something of a mutual-aid society (given Nandi's training).

Tabletop Games

 * The Forgotten Realms setting of Dungeons & Dragons has an unconventional take on this: the church of Sharess is mostly composed of prostitutes of all ends of the spectrum, including males, and while Sharess is only a demipower, the church has powerful allies and more influence in certain quarters than one would expect. Completely understandable in that Sharess is the goddess of pleasure (And going by her favored weapon, all flavors thereof).
 * Not quite on that last note: Sharess is Chaotic Good. Masochism and the like are the purview of Lawful Evil Loviatar, while other, darker, pleasures fall under the banner of Neutral Evil Shar. Sharess's angle is more humanitarian-both prostitutes and escorts who take pride in their professions, and those fallen into those professions who struggle to stay morally decent people.
 * The Old World of Darkness game Werewolf: The Apocalypse has the Aethera Inamorata, a faction within the Children of Gaia tribe composed of sexual healers. They're all about the spirituality of sex and maintains the tribe's close ties to the Cult of Ecstacy tradition of Mages. They were originally known as "Houris" and/or "The Hours," and claim that agents of the game's Cosmic Horror mutated that name into "whore" and turned sex into something seen as dirty and shameful by society.
 * In 7th Sea, "Jenny's Girls" are an important political group.
 * Some Warhammer 40,000 novels imply that institutionalized prostitution is relatively common.

Web Comics

 * In Drowtales, the Guild of Flowers.

Real Life

 * Truth in Television: There is such an organisation in the UK called the International Union of Sex Workers. They're part of the GMB, and I remember an article from a few years back about table-dancers joining the GMB as well, inspired by the example. (The GMB is Britain's General Union—basically a way for those who aren't part of the huge professions to have a chance at some representation at the higher levels).
 * There is also the English Collective of Prostitutes.
 * In general there are a lot of these, including the admittedly silly-sounding Canadian Guild of Erotic Labour and the International Sex Worker Foundation for Art, Culture and Education, which also focuses on the collection and preservation of art by and about sex workers.
 * Is CGEL pronounced "kegel"?
 * This is also dead serious in some South American nations; they want their rights.
 * The equivalent US organization is COYOTE, for Call Off Your Old Tired Ethics. Fun with Acronyms, indeed.
 * And the Finnish sex workers' organization is called SALLI. Salli is both a traditional woman's name and the second person imperative form of the verb "allow" in Finnish.
 * The German equivalent is called Hydra e.V.
 * ... you know what, I don't even want to know.
 * New Zealands Prostitutes Collective were instrumental in passing the Prostitution Reform Act 2003
 * One of the oldest ones is the "Rode draad" or "red thread" in the Netherlands. Being both a lampshade of the infamous red light districts and a Dutch-language pun on having something in common.
 * Even punnier: the Dutch word for sewing ("naaien") is slang for screwing. Yep.
 * And it is probably a play on the story of Jericho, where the whore Rachab put a red thread out of her window.
 * So they're seamstresses (hem, hem)?
 * Appropriately, the organization takes it's left-wing, or "red" roots very seriously. It is one of the powerhouses of Dutch politics, and has done valuable work in multiple areas, including law enforcement, workplace safety regulations and public healthcare reform.
 * Religious institutions have often taken on the role of "supervisor of the brothels," typically maintaining standards of cleanliness of facilities and ensuring the welfare of the prostitutes. In some cases, this was because the religious authorities held a "better allowed, safe, and under our control than prohibited, dangerous, and out of our hands" attitude towards the practice; in other cases, this was because the prostitution was a religious ritual/duty.
 * In London the brothels of Southwark were owned by the Bishop of Winchester.
 * But in Paris and Lyons in medieval France, they were part of the guild dealing with baths, which led to moral censors deciding to completely close the public baths in France as well in the 17th century.
 * Slightly further in the past, most of the... "quality" prostitutes were found in temples.
 * The term devadasi originally described a Hindu religious practice in which girls were "married" and dedicated to a deity (deva or devi). In addition to taking care of the temple, and performing rituals they learned and practiced Bharatanatyam and other classical Indian arts traditions, and enjoyed a high social status. Over time, the institution became identified with prostitution.
 * The temple prostitution of Ishtar is Older Than Dirt. Makes sense, as Ishtar was literally the goddess of sex.
 * And of War, but not of Childbirth.
 * The Sex Workers Outreach Project USA protested against Grand Theft Auto's use of Disposable Sex Worker.