A group of 200 large American corporations is urging the country's top court to strike down a law that restricts marriage to heterosexual unions, arguing it creates expensive human resources headaches with regards to employee benefits.

Companies including Google, Microsoft, Citigroup, Apple, CBS, Ernst & Young, Thomson Reuters, Nike, Xerox, Intel, Pfizer and Goldman Sachs signed their names to a brief in the case of Windsor v. United States.

That's a case that the Supreme Court will hear at the end of the month involving whether the survivor of a same-sex relationship whose life partner died would have to pay hundreds of thousands in taxes for inheriting her partner's estate — fees a heterosexual partner wouldn't face.

The case takes aim at the so-called Defence Of Marriage Act, a 1996 law that restricts the definition of marriage to a union between one man and one woman. On March 26 and 27, the Supreme Court will hear arguments in the Windsor case and one involving Proposition 8, the ballot initiative defending traditional marriage that California voters passed on election day in November.

'DOMA impairs employer/employee relations and other business interests'— Bingham McCutchen's brief

The Windsor case involves Edith Windsor and Thea Spyer, who married in Toronto in 2007 and had their marriage recognized by their home state of New York. When Spyer died in 2010, Windsor, 83, was hit with a $363,000 federal estate tax bill, one which a heterosexual partner would not have had to pay.

The 200 corporate signatories are part of a broader push by gay-rights groups to get the court to overturn the law. And while a significant gesture, the corporations that lent their names to the push strenuously noted their interest in the case is primarily a business one.

"DOMA, a federal law withholding marital benefits from some lawful marriages but not others, requires that employers treat one employee differently from another, when each is married, and each marriage is equally lawful," a brief by Boston-area law firm Bingham McCutchen reads. "DOMA impairs employer/employee relations and other business interests," reads the brief by Bingham, which is handling the case pro bono."

"DOMA enforces discriminatory tax treatment of spousal retirement and health care benefits," the brief reads. The companies say DOMA hurts businesses that operate across the U.S. because a handful of states already have some sort of gay marriage recognition, which creates a human resources nightmare to have to treat employees differently.

Tax implications

"In many other benefit-related matters, [DOMA] incurs the cost and administrative burden of 'workarounds' [employer-created benefit structures attempting to compensate for the discriminatory effects of DOMA]."

It also forces companies to discriminate against certain employees in terms of benefits, often in direct contravention of the company's internal policies.

The corporate brief accompanies other similar documents of a more political angle. Gay-rights groups have been busily recruiting politicians from both sides of the aisle willing to publicly push the court to overturn DOMA.

Among prominent Republicans joining in support of gay marriage are former presidential candidates Jon Huntsman and Gary Johnson, former governors Christine Todd Whitman of New Jersey and Paul Cellucci, Jane Swift and William Weld of Massachusetts and 2010 nominee for California governor Meg Whitman, who supported Proposition 8 in her campaign.

Also on the list are two members of Congress who voted for the federal law in 1996, Rep. Ileana Ros-Lehtinen of Florida and former Rep. Deborah Pryce of Ohio.

"This brief in some ways is a microcosm of what's happening all over the country, across political parties, as people examine their core beliefs and values," said Ken Mehlman, a former chairman of the Republican National Committee who came out as gay in 2010.

The Supreme Court has never given gay Americans the special protection it has afforded women and minorities. If it endorses such an approach in the gay marriage cases, same-sex marriage bans around the country could be imperiled.

With files from The Associated Press