ATLANTA — Gay rights advocates were surprised Thursday that the president of fast-food chain Chick-fil-A has taken a public position against same-sex marriage.

Chick-fil-A President Dan Cathy said this week that his privately owned company is “guilty as charged” in support of what he called the biblical definition of the family unit.

The Atlanta-based chain opened its first location in a Georgia mall in 1967 and grown to more than 1,615 restaurants in 39 states and Washington, D.C., with annual sales of more than $4.1 billion, according to its website.

“We are a family-owned business, a family-led business, and we are married to our first wives. We give God thanks for that,” Cathy told the Baptist Press, the news agency of the Southern Baptist Convention.

His comments unleashed a mix of criticism and support.

“He’s taking a bold stand,” said Tony Perkins, the president of the Family Research Council, which is based in Washington, D.C. “Chick-fil-A is a Bible-based, Christian-based business who treats their employees well. They have been attacked in the past about their stand. But they refuse to budge on this matter, and I commend them for what they are doing.”

Chad Griffin, president of the Human Rights Campaign that works for same-sex-marriage, said Thursday that Chick-fil-A “has finally come clean” after cloaking its positions for years.

“While they may have been in neutral, kicking this fight into overdrive now allows fair-minded consumers to make up their own minds whether they want to support an openly discriminatory company,” Griffin said in a statement. “As the country moves toward inclusion, Chick-fil-A has staked out a decidedly stuck-in-the-past mentality.”

Chick-fil-A released its own statement, saying it has a history of applying biblically-based principles to its business, such as keeping its restaurants closed on Sundays.

“The Chick-fil-A culture and service tradition in our restaurants is to treat every person with honor, dignity and respect — regardless of their belief, race, creed, sexual orientation or gender,” according to the statement.

“Going forward, our intent is to leave the policy debate over same-sex marriage to the government and political arena,” it said.