My employer has less than 15 employees, they do not hire males even though they apply for positions. Is this illegal for a company of this size?

I work for a local call center and have done so for almost 2 years. During the interview process, candidates are brought into the main work area for pre-employment testing (just to show they are able to navigate a computer and follow basic instructions). None of these candidates have been male but we frequently get calls from male job seekers who respond to the newspaper advertisement. We cannot tell them that they will not be considered for the position because they are male but there is no reason,to my knowledge, as to why they are not considered. I've been told by other employees that this has been the practice from 30 years ago when the company first started because it was a preference of a few of the clients. There are 10 employees who are staffed here including human resources, accounting and I.T. I am not sure if discrimination laws apply in this situation?