OLYMPIA, Wash. -- Amazon.com founder Jeff Bezos waded into a developing corporate culture war over gay marriage Friday with a $2.5 million donation to keep same-sex unions legal in Washington, becoming the latest in a list of high-profile executives to take public stands on a hot election issue.

Bezos joins Microsoft co-founder Bill Gates and companies like Starbucks and Nike with support to the campaign to uphold Washington's law. And while fast-food chain Chick-fil-A set off a furor opposing same-sex unions this month, other companies -- including big names like General Mills and Nabisco -- are brushing off fears that support for gay marriage could hurt their bottom line.

Gay rights advocates say the activism sends a strong message.

"Companies are a bellwether of what is in the mainstream," said Marc Solomon, the national campaign manager for Freedom to Marry, a New York-based group that advocates for same-sex marriage. "When you have some of the mainstays of corporate leadership stand up, that's important. It sends a powerful message about where our society is right now."

Solomon and other national advocates say the donation by Bezos and his wife, MacKenzie, is the largest publicly reported gift to support a gay marriage ballot measure, noting that some gay marriage opponents have tried to shield their donor lists.

Washington is one of four states with gay marriage measures on the ballot this November. Washington and Maryland both legalized gay marriage this year, but will also have public referendums this fall. In Maine, voters will decide on an initiative to approve same-sex marriage three years after voters overturned a state law. In Minnesota, voters will decide whether to pass a constitutional amendment to ban gay marriage.

Same-sex marriage is legal in New York, Connecticut, Iowa, Massachusetts, New Hampshire, Vermont and Washington, D.C.

Food giant General Mills, based in the Minneapolis suburb of Golden Valley, Minn., publicly spoke out against the state's proposed amendment that would ban gay marriage, as well as Thomson Reuters, and St. Jude Medical, and executives including the co-owners of the Minnesota Twins. Even more national brands -- Nabisco, J.C. Penney and Minnesota-based Target among them -- have stuck with recent, gay-themed advertising.

John Taft, CEO of RBC Wealth Management U.S., has pressed Minnesota companies and executives to oppose the state's proposed amendment, saying it's simply good business.

"We're all competing for talent, we're trying to recruit and retain the best people out there," Taft said. "If you're going to be successful in business, you have to do diversity well. The world is becoming more diverse, not less diverse."

Atlanta-based Chick-fil-A President Dan Cathy angered gay rights advocates this month with another position, saying the company was "guilty as charged" for backing "the biblical definition of a family."

Gay rights groups urged a boycott and the mayors of New York, Boston, Chicago and San Francisco spoke out against the chain; Christian conservatives promised to buy chicken sandwiches and waffle fries next week on "Chick-fil-A Appreciation Day."

In March, after a shareholders' meeting of Seattle-based Starbucks, the Washington, D.C.-based National Organization for Marriage announced a "Dump Starbucks" protest and called for a boycott of the coffee giant. Starbucks spokesman Zack Hutson said its business hasn't been affected.

Janet Bezdicek, a suburban Minnesota mother of five, said she's taken Cheerios off her shopping list because of General Mills' stance.

"We're talking about a definition of something that's been upheld for centuries. To be challenged by a corporation, that's not appropriate," she said.

But there's little evidence that a conservative-mounted boycott over gay rights issues has tanked a company's stock or made a noticeable dent in its profits, said Andy Bagnall, a New York City advertising executive who advises corporations on cultivating the gay community.