Wedlock Block

A couple or several couples are ready to get married, but they're not allowed to (probably because someone's parents won't allow) because someone else's nuptials (usually an older sister's) have to take place first. This can cause delightful complication if a lesser priority couple needs to Altar the Speed. Settle for Sibling is often the result of this.

Film

 * In the Bollywood film Sanam Teri Kasam, the conflict is kicked off because the heroine is the elder and most homely daughter of a very traditional household, her father won't let his younger daughter marry before the elder, and her younger sister isn't only desperate to marry to her fiancé, the guy puts her in a deadline of marrying before he goes to his new job abroad in a month or cancelling their engagement. The younger daughter eventually gets her wish of marry before her sister... but only because the efforts of the heroine to solve the situation end with her father disowning her and declaring her dead to them.
 * Not so much a Wedding Block as a Dating Block, but in 10 Things I Hate About You Bianca Stratford is forbidden from dating until her older, misanthropic sister Kat is herself dating a boy.
 * In 1982's The Pirate Movie (a semi-Mockbuster version of The Pirates of Penzance starring Kristy McNichol), one of the roadblocks on the way to true love is that Mabel, as the youngest of a baker's dozen, cannot marry Frederick until her older sisters are all married off first.

Literature

 * Found frequently throughout the works of Jane Austen. Though it is not required, it is considered highly improper if the daughters do not marry in order of their birth - the only time it's acceptable is if the older sister slips into the category of "Old Maid" around age twenty-three. Furthermore, it's considered unusual (as in Pride and Prejudice) to have the youngest daughter (of five) "out" (accepted as grown-up and eligible for marriage) before the eldest is married.

Live Action TV

 * 1981's The Brady Girls Get Married, one of The Brady Bunch spin-off TV movies, has the parents reluctant to officially approve Jan's marriage plans because Marcia is single. Marcia explains this problem to a random male stranger she meets... resulting in a Fourth Date Double Marriage with Jan and her beau.

Religion

 * The Ur Example is Jacob's story in The Bible, which play with this trope in that while Jacob wants younger daughter Rachel, Laban wants to marry off older daughter Leah off first, so tricks Jacob into marrying both of them in succession, securing seven more years of Jacob's labor for Rachel.

Theatre

 * In The Taming of the Shrew, Baptista will not give his younger daughter Bianca's hand in marriage before he finds a husband for Katherina, his shrewish older daughter.
 * In Once Upon a Mattress, a law forbids anyone in the kingdom from marrying before Prince Dauntless does.

Truth in Television

 * If you and your fiance get engaged around the same time as close mutual friends or relatives, someone will almost certainly have to wait, unless they agree to go for a double wedding option. This is not only to avoid Claire and Dan upstaging Alice and Bob, but also because of the expense the mutual friends and family would have regarding wedding gifts, bridesmaid dresses, etc.