In an "at will" employment relationship an employer can pretty much do as they please with respect to imposing work requirements or with respect to the hiring/firing on an employee. The fact is that the excuse of probation wasn't necessary. An employer can fire an employee for any reason or no reason at all. That is unless the employee has some legal protection afforded by an employment contract/union agreement or this action was be against company policy.  Also, if discrimination plays a factor, that too would establish certain legal employment rights.  Otherwise, termination under these conditions would be lawful. While seemingly unfair it is the law.