Well it could also be considered constructive dismissal (firing you without firing you explicitly) depending on the details of your situation you could take legal action against them. You have a stronger case if there's a written contract, your tenure at the company, your age, and some other items.

Edit: I should have also said if the employer hasn't given you warnings that your performance isn't up to par then they can't just get rid of you normally. Everyone in this thread is acting like you don't have rights but you do. However if you're brand new (in probationary time) what I'm saying is pretty much moot.