This is an interesting question and, with pool season upon us, a particularly timely one, since most party pools charge more for men than women.
The crux of this is at the heart of the same reasoning that allows casinos to "86" blackjack players for card counting, even though legally they're doing nothing wrong, namely that private organizations, including businesses, are not subject to abiding by the Bill of Rights. So, for example, there is no right to freedom of speech on private property and the owner has the right to ask you to leave whenever they like and for whatever reason they see fit.
Bars, nightclubs, and pools are not required to abide by the Fourteenth Amendment, which specifically applies to the State, not private entities. Under federal law, a business can charge anyone whatever cover they want to, whether it's based on age or gender, for example. That's what makes "Ladies’ Nights," senior discounts, and customer loyalty offers possible. A property can't discriminate on grounds of race, however, since that's covered by the Civil Rights Act of 1964, which prohibits "discrimination or segregation of any kind on the ground of race, color, religion, or national origin."
Some states, including California, Maryland, and Wisconsin, do have laws banning Ladies’ Nights and their attendant gender/pricing discrimination, although these laws are generally seldom enforced. In 2010 a men’s-rights activist named Den Hollander took on the Copacabana Nightclub and other venues in New York, claiming that their female-specific discounted pricing policies were gender-discriminatory. Hollander argued that since bars and nightclubs are licensed by the government to sell alcohol, that effectively makes them vendors on behalf of the state, and thus subject to the Fourteenth Amendment. He lost the case at the District Court level and his appeal was denied last August.
In other states where the concept has been challenged, including Illinois, Pennsylvania, and Washington, the concept of "Ladies’ Night" or differential gender pricing was found not to be in violation of local laws. Minnesota's Department of Human Rights declared last year that bars are discriminating against males by holding "Ladies' Night" promotions, but said it will not seek out participating establishments to enforce this ruling. In Nevada, the concept has yet to be tested legally, but with so many varied promotions taking place all over town throughout the year, we imagine it's a can of worms that no one will want to open.
While we can appreciate the justification of observing that a two-tiered price structure based on gender is discriminatory, the policy is there not least to ensure that women -- who presumably constitute the primary reason for the majority of males attending bars and clubs -- will be encouraged to attend in sufficient numbers to keep the gender ratio about equal. From a female point of view, the higher cover charge for men at topless pools affords at least some protection from those males who simply want to show up and gawk at bare breasts, the attentions of whom are not conducive to relaxing sunbathing.
