Benefits are not mandatory. What job title do they have? Is it EXACTLY the same as yours? When you were hired, was the job classified as being a "non benefit" position? The only legal standard is that if you do exactly the same job, for exactly the same length of time, with exactly the same performance reviews, with exactly the same educational/work experience background as a non-protected (white male), then you are entitled to equal pay. Benefits are in NO WAY SHAPE OR FORM considered compensation and therefore are not subject to equal pay laws.
My husband works for a small company. All of the managers are male (3 of them are partial owners) and everyone at the "management level" receives 100% paid insurance. All of the admins are female and also work in the office but they are not classified as management and; therefore do not receive benefits