Gays and lesbians puckered up at 'kiss-ins' outside Chick-fil-A outlets across the United States in protest over the fast-food chain's opposition to same-sex marriage.

More than 14,000 people signed up on Facebook for National Same Sex Kiss Day at Chick-fil-A on Friday, an event arranged mostly online.

"It has nothing to do with us being against freedom of religion or freedom of speech," Bryan McIlroy, a 35-year-old interior designer, told agencies outside a restaurant in the Hollywood area of Los Angeles.

"I'm here because I am gay and I don't think it's right to support any kind of hate. For somebody who claims that it's all about love, they sure are not showing it," said McIlroy, holding a sign that read 'Support love, not hate'.

"Jesus ate fish," read the sign of another Hollywood protester.

With more than 1,600 outlets, mainly in the southern United States, family-owned Chick-fil-A is as famous for its Bible Belt values -- it never opens on Sunday -- as it is for its chicken sandwiches and nuggets.

But it is under fire from gay rights activists and their supporters who, citing tax records, say it has given millions of dollars to conservative Christian groups that vigorously campaign against marriage equality.

"Guilty as charged," Chick-fil-A president Dan Cathy told a Baptist publication last month, adding in a subsequent radio interview that the United States is 'inviting God's judgment' by recognising same-sex vows.

Same-sex marriage, legal in six US states, is a hot-button issue among Americans this election year, with President Barack Obama in favor and his Republican rival Mitt Romney opposed.

Earlier in the day, activists installed a same-sex kissing booth outside a Chick-fil-A restaurant in Dallas.

"We want to show the country and the Chick-fil-A company that our love is just as valid, just as real and just as good as heterosexual love," organiser Carly McGehee said by telephone from the Texan city.

"And we deserve the right to be protected under the law, to raise our families and love who we want to love regardless of gender."

In a statement Friday, Chick-fil-A seemed unperturbed by National Same Sex Kiss Day, saying it appreciated 'all of our customers' and was glad to serve them at any time.

"Our goal is simple: to provide great food, genuine hospitality and to have a positive influence on all who come into contact with Chick-fil-A," said Steve Robinson, executive vice-president for marketing.

Two days ago, Chick-fil-A enjoyed record sales when loyal customers turned out in big numbers for a 'Chick-fil-A Appreciation Day' promoted by Republican politician and talk-show host Mike Huckabee.

"They are pure evil and hatred," said 40-year-old artist Steve Lanasa, who also protested at the Hollywood outlet.

"For them to spend so much money on a campaign to try to remove rights from other people who don't affect them at all is nothing but evil and intolerance and backwards."

In Atlanta, Georgia, where Chick-fil-A is headquartered, small-business owner Marci Alt invited the company's boss for dinner with her wife Marlysa and their two young children to experience the 'pretty normal life' they live.

"We care deeply about our faith, our family, our friends and our community, and think there's room to turn this debate into a dialogue," she said reaching out to Chick-fil-A president Cathy in an online petition on Change.org.