An "at will" employer can set the conditions of the worklace much as it sees fit. That is unless this action violated the terms of a union agreement or employment contract. Also, it must not constitute some form of legally actionable discrimination (which you did not indicate). Accordingly, if you could not pass the test and/or could not afford to take it again, our company was within its rights to terminate your employer. In fact, an employer can fire a worker for any reason or no reason at all.