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I'm very sorry to hear about your situation. First of all, you need to understand that Pennsylvania is an "at will" employment state. At-will employment means that without a contract, you have no contractual or other right to employment with the company. The company is entitled to fire you for any reason: a good reason, a poor reason, or no reason at all--as long as the company does not fire you for an illegal reason (race, gender, age, religion, etc...). But it extends beyond firing, to hiring, promotions, demotions, wage cuts and raises, disciplinary actions, and even scheduling. Unless you can show that this was done in violation of a contract, union agreement, or a clear violation of an unambiguous and binding clause against the employer, or that it was done because of some minority status (age, race, gender, religion, disability) that you have, then they do have this discretion.
If you have any evidence that you were targeted due to your race, age, religion, gender or disability, you could potentially have a case. But even if you were made "permanent", the employment would still be at-will. Only if you could establish a written contract that guaranteed you a position for a specific period of time could you have a case based upon that breach. A gratuitous promise is not actionable, even when you give up other opportunities.
I agree that these actions were unethical, immoral and illogical, but that doesn't mean they're illegal. I know this is probably not what you wanted to hear, but it is the law. I hope that clears things up anyway. If you have any other questions, please let me know. If not, and you have not yet, please rate my answer AND press the "submit" button, if applicable. Please note that I don't get any credit for the time and effort that I spent on this answer unless and until you rate it positively (good or better). Thank you, ***** ***** luck to you!