Assuming you do charge a cover for men, this is a really good way to get sued.
See Angelucci v. Century Supper Club, 158 P.3d 718 (CA 2007) and http://en.wikipedia.org/wiki/Ladies_night#California
Illinois gets it. California doesn't. Way to be the state with the stick up your butt again, CA.
Regardless of whether it should be legal or not, "positive discrimination" is still discrimination.