I suggest that you take your copy of the supposed contract to an employment law attorney who represents employees in disputes with their employer. Just because you signed that agreement doesn't necessarily mean that you have a contract with the employer. These agreements are often not enforceable as contracts because they lack mutual consideration. Consideration is something you give up in exchange for something from the other party. A number of courts have held that an employer offering continued employment is not, by itself, sufficient to count as consideration. So the first thing you need to find out when consult that attorney is if there is an enforceable contract at all.
If there isn't a binding contract between you and your employer then you are simply an at will employee and may be fired at any time for almost any reason. The reason doesn't have to be a good one. All that matters is that the reason isn't one of the relatively few reasons prohibited by law. The most common prohibited reasons are terminating you because:
(1) of your race, color, religion, sex (including sexual orientation, gender identity, etc) national origin, citizenship, age, disability, or genetic test information under federal law (some states/localities add a few more categories like marital status, veteran status, etc);
(2) you make certain kinds of reports about the employer to the government or in limited circumstances to specified persons in the employing company itself (known as whistle-blower protection laws);
(3) you participate in union organizing activities;
(4) you use a right or benefit the law guarantees you (e.g. using leave under FMLA);
(5)you filed a bankruptcy petition;
(6) your pay was garnished by a single creditor; and
(7) you took time off work to attend jury duty.
The exact list of prohibited reasons will vary by state. The Washington state Department of Labor and Industries page on termination and retaliation explains the laws that apply in that that state. explains the laws that apply in that state.
If there is an actual employment agreement in place, then the exact language of the contract matters as to when and for what reasons you may be terminated. Does the document say anywhere that you are guaranteed employment for some period of time (e.g. one year) except in circumstances that are specified in the contract? This is also something to speak to the employment law attorney about.