If you have an employment contract, you are not an at-will employee. The employment contract will generally define the reasons for which you can be terminated – usually, for “just cause” or other “legitimate, job related reasons. However, if your contract specifically states you are an employee at-will, you fall under the same rules as an at-will employee – you can be fired for any reason.
Employment contracts do not have to be in writing, however. An employment contract can be written or oral, or even based on a promise made by your employer, such as a promise that you wouldn’t be fired, that your job would be secure, of a promise that you’d be working for a certain period of time.