Because the spousal-protection law is federal, it does not apply to same-sex couples, whose marriages are not recognized for federal legal purposes. The law also does not cover Individual Retirement Accounts, or I.R.A.’s, Mr. Hohl said, although in some states, a state property law might give a spouse some protected interest.

Under the Retirement Equity Act, the consenting spouse’s signature on the required form has to be either notarized or witnessed by a plan representative. Many people come across such rules when they retire and choose a payment option, or when they want to change the beneficiary of a defined-contribution plan.

That could happen, for instance, when someone entering a second marriage wants his or her pension benefits to go to children from the previous marriage, and the new spouse is perfectly comfortable with that decision.

Or an estate planner might want to make an entity other than the spouse the pension’s beneficiary, with a spouse’s approval, for tax or estate-planning reasons, according to Gloria S. Neuwirth, a trusts and estates lawyer at Davidson, Dawson & Clark in New York.

One example Ms. Neuwirth gave involved a couple who want to give money to charity. “If you name an individual as beneficiary, then when they withdraw that money they have to pay income tax,” she said. “But a charity obviously doesn’t pay any income tax. So this would be advantageous where the couple wants to make a charitable gift” of a lump sum pension distribution.

Another example Ms. Neuwirth gave was a couple who will not need the money from a specified pension in their lifetimes. They might want to use the assets to set up a trust for one or more children, either minors or adults.

Because of the wording of the pension law, there are pitfalls in well-intentioned maneuvers if a lawyer is not supervising them. For example, Mr. Hohl at Fidelity said, “the definition of ‘consent’ and ‘beneficiary’ can vary depending on an individual’s situation, so investors should be very clear on these terms in order to ensure they are accomplishing their intended objective.”