Microsoft and Nike are among the 6 companies who on Thursday endorsed an effort to make Washington the seventh state to legalize gay marriage.

In a letter to Governor Chris Gregoire, the companies wrote: “We write you today to show the support of our respective companies for SB 6239 and HB 2516 recognizing marriage equality for same-sex couples.”

Washington state-based Vulcan, RealNetworks, Group Health Cooperative and Concur also signed the letter.

In a follow-up statement, Microsoft added that not allowing gay marriage could leave Washington companies at a competitive disadvantage: “Washington's employers are at a disadvantage if we cannot offer a similar, equitable and inclusive environment to our talented employees, our top recruits and their families.”

The proposed legislation, which is scheduled to get its first hearings in the House and Senate on Monday, also got a boost with the endorsement of Senator Jim Kastama, who once opposed gay marriage. The measure remains one vote shy of passage in the Senate.

Senator Ed Murray, the bill's sponsor in the Senate, called the endorsement a “significant step.”

“It's a significant step. But having lived through trying to find that last vote on the gay and lesbian civil rights bill, I am not yet ready to celebrate,” Murray told The Seattle Times, referring to a 2005 bill that failed by one vote in the Senate.

Opponents of marriage equality called Microsoft's support “inappropriate.”

“They are a software company, not a PAC, and the only reason they take a position and essentially stick a finger in the eye of their customers is that they think life would be too miserable if they don't,” Joseph Backholm, executive director of the Family Policy Institute of Washington, told the paper.