Only one group of employees were given a pay cut and no one else in the company had to take a pay cut is this discrimination?

Giving pay cuts to a job classification (e.g. nurses) is not illegal discrimination, since employers may treat different jobs or professions differently. It's also not illegal to cut the pay of one group or unit or department, etc. at work. However, giving pay cuts to women and not men may well be  illegal discrimination, since an employer may not pay women and men differently or cut the pay of women and not men. While there was one man, since he represented only 3% of the employees whose pay was cut, the cut overwhelmingly affected women; this may be discrimination and it is likely worthwhile to file a complaint with the Equal Employment Opportunity Commission. It is *possible* that the employer will be able to show that there is some valid non-discriminatory reason for this cut--e.g. this particular group was working on a drug or product where sales were down or declining; or HR had done a salary survey of the industry and discovered that this company was significantly overpaying employees doing this job and they reduced salaries to bring their pay structure in line with industry norms; etc.--but if the company cannot point to objective, verifiable, and non-gender-discriminatory reasons for the cut, the female nurses may have a viable discrimination claim.
(Note: actions predominantly affecting one gender are permissible so long as there is a legitimate, veriably reason for it which has nothing to do with gender.)