The statement, published Tuesday by The Seattle Times, describes Starbucks' commitment to a diverse and tolerant workplace.
"We are deeply dedicated to embracing diversity and treating one another with respect and dignity, and remain committed to providing an inclusive, supportive and safe work environment for all of our partners," the company said.
Starbucks joins other Washington state companies including Microsoft in showing support for the bill. The New York Daily News reports Washington would be the eighth state to recognize gay marriage if the bill should pass.
"It's time, it's the right thing to do," Gov. Chris Gregoire said in a statement on her Web site. "I say that as a wife, a mother, a student of the law and above all as a Washingtonian with a lifelong commitment to equality and freedom."