A recent Eight Circuit case is illustrative of what is meant by unequal pay under the Equal Pay Act.  In the case at point, there was no dispute as to whether or not there was equal work, as the suit followed the female HR director being promoted to another position at a salary of $45,600 where her new HR replacement, a male was hired from outside the company at an annual salary of $62,500.  Once we have an employee able to show that an employer paid different wages to men and women for performing equal work, the burden shifts to the employer to prove one of the four statutory defenses; (1) a seniority system; (2) a merit system; (3) a system that measures earnings by quantity or quality of production; or (4) a differential based on any factor other than sex.

In this case it was only the fourth category that could be any possible defense for the employer.  In general, it was unsuccessful as they certainly articulated legitimate non-discriminatory reasons for the employment action, but pay differential must be shown to be based on a factor other than sex.  The fact that this new candidate could demand a higher salary was, as a matter of law, determined to be insufficient. 

Drumm v. Leeson Electric Co-op Corporation (8th Cir. 2009).