Tech giants including Apple, Facebook, eBay and Intel have expressed their support for gay marriage in statements to the US Supreme Court.
California's Proposition 8 bans gay marriage, while the Defense of Marriage Act prohibits legally married gay couples from claiming federal tax breaks and other benefits available to opposite-sex spouses.
The companies are arguing that both are unconstitutional under the Due Process and Equal Protection Clauses.
"The briefs explain to the Court how the Defense of Marriage Act and California's Proposition 8 discriminate against employees in same-sex marriages and create undue burdens on companies and employees," says Facebook on its LGBTQ@Facebook page.
More than 60 companies are believed to have signed up to the brief, including Cisco, Oracle, Panasonic, Qualcomm, Xerox and Zynga. They will present their arguments on Proposition 8 to the court on March 26th, and on the Defense of Marriage Act the following day.
The companies are arguing that allowing gay marriage isn't just about human rights - it's good for business too. Gay couples, they argue, are more likely to want to work in states or countries where they're not treated as second-class citizens.
""By singling out a group for less favorable treatment, Proposition 8 impedes businesses from achieving the market's ideal of efficient operations—particularly in recruiting, hiring, and retaining talented people who are in the best position to operate at their highest capacity," they say.
"Amici are competing domestically and internationally with companies inside and outside the United States in places where all couples, regardless of whether they are of the same sex, are afforded equal access to marriage."
Currently, six states, plus the District of Columbia, allow same-sex marriage, and two others have enacted legislation that will come into effect this fall if approved in referenda.