A club representative dismissed his questions about the disparities, said Mr. Phillips, a lawyer who specializes in gender bias cases, so he filed a complaint with the Nevada Equal Rights Commission, arguing that price breaks and special areas of the health club for women only were illegal under state law. A ruling is expected shortly.

The complaint is perhaps the first anti-male gender bias case in Nevada, but civil rights panels and courts in several other states have grappled in recent years with what has come to be known informally as Ladies’ Night law because it often involves policies and practices among bars and nightclubs. Results have been mixed.

In 1985, the California Supreme Court ruled that such disparities were illegal, effectively ending them. Judges in Colorado, Iowa and Pennsylvania all have said that such events and offers are illegal, but state courts in Illinois and Washington have concluded that they are a permissible means of attracting desired customers.

The Nevada Legislature banned sex discrimination in 2005. Now, Mr. Phillips said, it is time for the ban to be enforced. Should the Equal Rights Commission rule in his favor, the gym would have to comply or file a lawsuit in District Court seeking to overturn the decision.

“Imagine a whites-only country club or whites-get-in-free deal or something like that,” said Mr. Phillips, 45, who has homes in Nevada and California. “When things are based on race, we have kind of a knee-jerk reaction because we’ve had poor race relations in America for 400 years now. But when it comes to treating people the same based on sex, that’s much more recent in our memory.”

The Las Vegas Athletic Club’s executive vice president, Chad Smith, defended the company, which owns five gyms in the area, saying he thought the law referred to public accommodations but not private clubs. (The law that defines public accommodations, however, includes “any gymnasium, health spa, bowling alley, golf course or other place of exercise or recreation.”)

Mr. Smith said that the club’s occasional discounts for women were to encourage them to exercise and that special workout areas for women were there to compete with Curves, the women-only chain of gyms.

“Our men are very, very happy with how we conduct our business,” Mr. Smith said. “This particular person is the only one who has had a problem with it. There are legitimate discrimination issues out there, and I wish he’d spend his time addressing those that really need addressing.”

That is a common response, said Prof. John F. Banzhaf III, a professor of public interest law at George Washington University Law School in Washington and a pioneer in fighting sex discrimination.

“I’ve had women students who didn’t like these ladies’ nights because one said it perpetuated a stereotype that women are less than men and need special assistance financially,” Professor Banzhaf said. “Another said she objected to the idea that they’re using these deals to get drunken women into bars to lure men into bars to attempt to pick them up. That is very objectionable.”

The casinos’ nightclub industry is watching the case carefully and awaiting the ruling on Mr. Phillips’s complaint because several clubs routinely offer free or reduced admission to women; a recent promotion for the Body English nightclub at the Hard Rock Hotel and Casino boasted that “ladies dressed in schoolgirl outfits drink free Champagne all night.”

No one from Body English returned calls for comment, but other club executives defended the discounts, especially when they are part of a promotion, not an ongoing practice. Promotions like these offer male customers the mix they seek, said Alan Feldman, a spokesman for MGM Mirage, which owns several nightclubs in its 10 resorts on the Las Vegas Strip.

“I don’t think these antidiscrimination laws had any intention of preventing something like this,” Mr. Feldman said. “In the circumstance of, Tuesday night is ladies’ night, that is a business decision by individual businesses and they ought to be left free to do that.”

But others were less concerned. Randy Maddocks, marketing manager for the House of Blues at the Mandalay Bay Resort and Casino, said he doubted his club would take a hit if he had to cease admitting women free.

“It’s one of those marketing techniques that is pretty much accepted, but I could also see the other side of it, too,” Mr. Maddocks said.