A Brooklyn bar owner says he’s going “straight” out of business — because his landlord won’t let him turn his watering hole into a gay bar.

John McGillion says he wants to transform Lulu’s to take advantage of a growing gay and lesbian community in the neighborhood.

But there’s just one problem: his lease specifically prohibits McGillion from running a gay bar.

“I am barely scraping by on the proceeds of the bar . . . If I am permitted to operate a gay bar at the premises I believe that I will be able to make a considerable profit,” McGillion said in Brooklyn Supreme Court papers filed last week.

Greenpoint was up and coming when John McGillion opened Lulu’s back in 2005, just a block from the East River.

He added two mezzanine levels and “put a lot of money” into the business, McGillion said.

Still, the joint “lost money, there’s no doubt,” he told The Post.

McGillion, who owns a handful of other bars in Brooklyn and Manhattan, believes he could have done another “40 to 50 percent” more business as a gay establishment.

McGillion has withheld the rent for months and has been battling landlord Guard General Merchandise Corp. for more than a year over the issue, but says it won’t budge.

“I don’t know what their problem is. Who knows? I thought those days were gone,” he said of the lease. “I mean, who cares, today? Gays — everybody’s got their rights. What’s the big deal?”

Fed up, he tried to sell the business on three or four occasions, but the deals fell through when the landlord, identified in public records as Janet Berger of Manhasset, tried to triple the rent for the prospective buyers, he claims.

“When we went in there 10 years ago we were taking a big risk. Ten years later there’s a big, big difference. Their property is a lot more valuable,” he said.

Bars catering to gay customers have a big upside, McGillion said.

“They do well because you don’t have issues of fighting,” he said. “They’re nice people, they’re wonderful to deal with. It’s easier. Typically you don’t have to offer food.”

But with just 10 months left on the lease, McGillion is asking a judge to declare the controversial clause invalid, and to instead extend the deal by two or three years

The landlord declined to comment on the litigation.