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 Inc. and Nike Inc. 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. And 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 Inc., 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 earlier this month with another position, saying the company was "guilty as charged" for backing "the biblical definition of a family." He later added, "I think we are inviting God's judgment on our nation when we shake our fist at him and say, 'We know better than you as to what constitutes a marriage.'"

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."

Conservatives have also targeted companies in the Pacific Northwest that threw public support for the Washington law allowing gay marriage, up for a statewide referendum in November.

In March, following 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.

Last month, Gates and Microsoft co-founder Steve Ballmer donated $100,000 apiece to the campaign defending gay marriage. Keeping the law in place "would be good for our business and the state's economy," Microsoft spokeswoman Serina Hall said in an email.

In Minnesota, a number of executives have donated large sums to defeating Minnesota's amendment that would ban gay marriage. State law already outlaws gay marriage, but supporters say the amendment is needed to fend off future legal challenges.

Jim, Bill and Bob Pohlad, the brothers whose holdings include the Minnesota Twins, together donated more than $300,000 to defeat the amendment. General Mills CEO Ken Powell personally donated $10,000, as did Michael Davis, the company's senior vice president for human resources. Greg Page, the CEO of agribusiness giant Cargill, donated $1,000, while Doug Baker — the CEO of chemical products company Ecolab — donated $500.

All those executives declined interviews on the marriage amendment. Powell announced the company's position last month at an internal gay pride function; Ken Charles, the company's vice president for global diversity and inclusion, elaborated in a blog post.

"We believe a diverse, inclusive culture produces a stronger, more engaged workforce," Charles wrote. "Inclusive communities are more successful economically as well."

Other companies, including Target, have financially supported gay rights groups and courted gay customers — but stopped short of directly calling on Minnesotans to vote against the amendment.

"Marriage equality is still a lightning rod issue in this country, and the country is still divided on it," said Andy Bagnall, a New York City advertising executive who advises corporations on cultivating the gay community. "Any corporation that's going to step into that, they really need to be prepared for what the response is going to be."

Recent demonstrations against General Mills drew opponents who turned in their boxes of Old El Paso taco shells and cans of Green Giant corn and other General Mills products.

Janet Bezdicek, a suburban Minnesota mother of five, said she's taken Cheerios off of 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, Bagnall said. Companies including Disney, Home Depot and Kraft Foods have been past targets of pressure by socially conservative groups for outreach to gay customers.

Bezdicek, who lives in Plymouth, Minn., and brought three of her kids to the demonstration, said she tries to shop with companies that share her values but said it's becoming more difficult to line up her purchases with her conscience.

"My mother and I are always saying we're not going to have any place to shop anymore," she said.

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Patrick Condon reported from Golden Valley, Minn. Doug Glass contributed from Minneapolis.

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