You probably cannot make a legal challenge to the fact that your female coworker received a raise under questionable circumstances. The question is whether you were denied a raise or receive less pay because you are male. If you can prove that, you may have a case of sex discrimination under Title VII of the Civil Rights Act of 1964, and, possibly, under state employment discrimination laws. The elements of a prima facie case under Title VII are: 1) You are a male, 2) you performed your job up to the employer's reasonable expectations for receiving a raise, 3) you were denied a raise, 4) a less qualified female coworker, similarly situated, received a raise. If you meet these elements, the employer would have to articulate a legitimate business reason for why you did not get the raise. If the employer articulates such a reason, you must prove that the reason given by the employer is not worthy of credence or that intent to discriminate based upon your gender was the actual reason.