If you think prenups are controversial, brace yourself. Postnups are on the rise.
Postnuptial agreements—similar to prenups, but for married couples—are gaining acceptance, with nearly all 50 states now allowing them. The agreements can cover everything from how to divide financial assets in divorce to limits on partners' weight gain, just as prenups can. And in a survey of divorce lawyers by the American Academy of Matrimonial Lawyers, 51 percent saw an increase in postnups and 46 percent saw no change from 2009 to 2012.
Now that the Supreme Court has struck down the Defense of Marriage Act, or DOMA, experts say more postnups could be in the offing.
It's not because newly married same-sex couples' unions are likely to suddenly founder. On the contrary: They will need to reallocate some of their property now that they can tie the knot, according to Marilyn Chinitz, a partner at Blank Rome.
"You can anticipate that couples are going to want to address property rights in a postnup for property that otherwise would have been deemed separate, because they acquired it before the marriage," she said. "Many couples will want to give recognition to those assets and put them in the marital estate."
Chinitz said DOMA's demise could lead to a moderate pickup in postnups. But Randall Kessler, a partner at Kessler & Solomiany and past chair of the American Bar Association's family law section, expects a surge in both prenups and postnups.
"Now that federal and related benefits cannot be denied to a same-sex spouse based on DOMA, those who have the benefits may want to protect them," he said. And couples who have rushed to marry in the wake of the ruling "may not have wanted to delay the wedding to have to negotiate a prenup. But they can still get a postnup."
(Read More: Being Financially Prepared for DOMA Ruling)
Kessler says couples come to him for postnups for three main reasons: They ran out of time to put together a prenup, they are trying to give their marriage a last chance or one party receives a large gift or inheritance, such as a family vacation home, with strings attached.
Sometimes a postnup winds up simply making a divorce agreement easier to reach. Rupert Murdoch and his wife, Wendi, signed a postnup after each of their two daughters was born, so the courts will decide how those might apply.
(Read More: Why Your Prenup May Need a Postnup)
"The point is to try to help people stay married, to separate their financial concerns from the fact that they love each other and want to stay together," Kessler said.
Chinitz echoed that. "You see postnups when the marriage is deteriorating and they don't want to get a divorce per se, and they want to right the wrongs," she said. Postnups may also come in handy for trust fund babies. "You also see it for young people who are likely going to inherit a lot of property but they don't have it yet."
Then there are the cases in which a spouse has done somebody wrong and wants to make concessions to keep the marriage together. Chinitz said she is negotiating one such agreement right now.
Whatever the reasons for postnups, they seem to be here to stay, not least because they are one of the few tools couples have to remove big money issues from their arguments.
"If you take money out of the equation, a lot of marriages would work," Kessler said. "Money causes a lot of problems."
—By CNBC's Kelley Holland