If, as many legal experts predict, the Defense of Marriage Act is struck down by the Supreme Court, advocates behind the decadeslong movement for gay rights will have won a major victory. But the decision could also create a dense legal maze for gay and lesbian married couples, one that would surely lead to more lawsuits that could make their way back to the Supreme Court.

And striking down DOMA would not just affect same-sex couples, but their employers. Basically, said Jonathan Zasloff, a professor at UCLA School of Law, the result could be a “mess.”

The problem resides in conflicting state gay marriage laws and how the federal government would interpret them. Last week, the court heard arguments about whether Section 3 of DOMA—which prevents the federal government from recognizing same-sex marriages—is unconstitutional. Justice Anthony Kennedy, generally the court’s swing vote, seemed inclined to strike down the statute on the grounds that it interferes with states' rights to define marriage, raising hopes among gay rights groups that thousands of married same-sex couples will be able to access the federal benefits of marriage for the first time.

If DOMA is struck down, then same-sex couples residing in states that allow gay marriage will suddenly be included in the more than 1,100 federal laws that give benefits to married couples. Gay couples, for instance, could file jointly on their tax returns, apply for Social Security survivor benefits if their spouse dies, and take up to 12 weeks off to care for a sick family member without fear of losing their job under the Family and Medical Leave Act.

But what about a gay couple that gets married in New York and then moves back to North Carolina, or any other of the 38 states that have explicitly banned gay marriage?

At first glance, it appears they would have no access to these rights, and that their marriage would not be recognized either by their state or the federal government. During oral arguments, Justice Samuel Alito asked attorney Roberta Kaplan, who was arguing against DOMA, this very question. Alito asked whether a New York gay couple who moved to North Carolina could qualify for the same federal estate tax breaks that heterosexual married couples enjoy if one spouse dies.

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"Our position is only with respect to the nine states ... that recognize these marriages," Kaplan responded.

In Kaplan's version of events, the Supreme Court could strike down DOMA and essentially create two different worlds for gay married couples in the country. In a handful of states, gay couples would enjoy all the benefits of heterosexual couples, but if they moved to the majority of the states in the union, their marriage would effectively disappear—for both federal and state purposes.

But Zasloff doesn’t think that will pass muster. He predicts same-sex couples would sue the government, arguing that this policy violates their constitutional right to travel. (In the past, the Supreme Court has struck down states’ waiting periods for new residents to enroll in welfare programs, holding that they violated the right of interstate travel.) Same-sex couples could also make a broader legal argument that the federal government should define “marriage” based on where a couple got married, not where they currently live.

The Supreme Court could sidestep this inevitable legal battle by explicitly noting whether the federal government should recognize same-sex marriages if the couples are no longer living in states that issued their license. But some experts say don’t count on it.

Andrew Koppelman, a professor at Northwestern University School of Law, says he would be "astonished" if the Supreme Court clarified the issue in its opinion. Zasloff agrees, noting that Kennedy, who will most likely write the DOMA opinion if it is struck down, is known for his sphinxlike unwillingness to expound upon the details in his opinions.

That would leave broad discretion to the Obama administration to define the issue administratively, Koppelman says. The White House could direct federal agencies like the IRS to accept marriages based on where a couple got married, not where they live.

Should the Supreme Court justices spell out that same-sex marriages are not valid in states that don't recognize them, the legal differences between married same-sex couples in different parts of the country would be stark.

Under that scenario, Todd Solomon, a partner at the Chicago law firm McDermott Will & Emery, who focuses on employee benefits issues, predicts a gay-couple migration to the nine states (and the District of Columbia) that allow the unions, since Social Security, tax and other federal benefits are at stake.

Cathy Stamm, a consultant at Mercer, a human resources firm, said employers are also anxious to see what the Supreme Court will decide. She's advising firms to comb through their benefit plans that involve employees' spouses—anything from health insurance to pension plans to employee discounts—to figure out whether state or federal law will require them to cover same-sex spouses if DOMA is struck down. Solomon predicts that employees in same-sex marriages may sue employers if they deny certain benefits to their spouses if this happens.

Employers might face a particularly tricky situation if they’re based in an area that allows same-sex marriage but their employees commute in from a state that does not. So, for example, would an employee with a same-sex spouse be eligible to take 12 weeks of family leave if he or she lives in Virginia but works in D.C.? Even though Virginia doesn't allow same-sex marriage, most labor laws are based on where the place of work is, so there's no simple answer. Stamm says employers hope the Supreme Court will help them avoid this legal thicket.

"There's a lot of confusion about what employers need to do," Stamm said. "I think employers would welcome some guidance from the court when they provide their ruling."