The ladies call themselves "BBW" or "big, beautiful women". The gentlemen are known as "BHMs'" or "big, handsome men". Their common interest, when they're not pounding the specially reinforced dancefloor, is the noble cause of "size acceptance".

With a black president in the White House, and laws protecting gays, women and religious minorities, America's nightclub scene is fostering a new movement to secure civil rights for one of the few social groups who can still legally be persecuted: fat people. An explosion of 'plus-size' entertainment venues, where revellers of all shapes and waistlines are welcomed, is managing to tap both the economic and political potential of the country's one in three adults who are clinically obese.

In Long Beach, California, Lisa Marie Garbo, who styles herself as the voice of America's BBW "community", has begun inviting patrons at her Club Bounce to sign petitions calling for President Obama to include the overweight in proposed new employment and hate-crime laws.

She is busily spreading the word among the 400 like-minded punters who attend her venue every Friday and Saturday. "In most nightclubs, overweight people get laughed at, treated like dirt and made to wait in line for hours by doormen. We're a feel-good club: a place where anyone can come and learn to feel good about themselves."

Garbo (41) whose weight has varied, over the years, from 19 stone to 23 stone, is a descendant of the film star Greta, whose sylph-like quality was never in doubt. She was inspired to open Club Bounce after being refused entry to a Hollywood nightspot, and now plans to roll out a chain of franchised venues across the country.

"People think being overweight is a choice, and have historically used that as an excuse to deny us rights. But it's not always down to that. I'm asthmatic. I was put on steroids when I was young. I'm not a perfect eater, and I don't exercise every day, but there are other factors making me the size I am, and it should never be used as an excuse for discrimination."

Roughly 70% of her male guests, and 30% of female ones, are "normal sized", she estimates. Many of the "smaller punters" pay the $15 (£10) entrance fee in order to have a chance of meeting an attractive, larger member of the opposite sex. "A lot of normal-sized people are attracted to overweight people. They celebrate them," she said

Most of the nation's handful of "plus-size" venues were started in the last couple of years, to cater for a community that grew up around internet chat-rooms. To many patrons, they provide a form of therapy, helping social lives that were previously non-existent.

"I see myself as a stepping stone," says Kathleen Divine, who owns the Butterfly Lounge in Orange County. "A lot of people who come along might never normally go out because of their size. The more they enjoy themselves here, the more confidence they get. It can really help their self-esteem. I've had people tell me that this club persuaded them to go out and get a better job."

Divine has recently widened her business empire to include a dating site for BBWs, together with a fashion label called Big Girl Gear, which sells nightclub clothing for larger women. "There's huge demand for what we do. People have flown in from San Francisco, Las Vegas, and even the UK and Australia. You would be amazed by what happens on the dancefloor."