I recently quit a salaried job in Texas and was told by the employer he was deducting 1 days pay form the salary since I had "used a sick day without getting his permission beforehand" which was not in my contract. He also only sent half of the final paycheck and that if I cash the partial check I can not file a workforce claim (I brought up the possibility when he said that he would only pay a partial paycheck). Is this true? I could use the paycheck but don't want to give up the other half because I cashed the one he sent. I have the contract which says nothing about him being able to change the terms because I quit.

If pay was deducted in violation of your contract, assuming it is a bona fide, enforceable contract, and not just an offer letter or a statement of terms of employment, you have a contract issue, not a wage and hour issue, and such a contract should include wording about what legal recourse you may have if it is breached.

Regarding your pay, the final paycheck for employees who resign is the regular payday; no acceleration of the paycheck is required under the law.

I had an offer letter rather than a contract but he isn't paying me for the full hours worked and the paycheck is over a week past due. My main question would be his statement that by cashing the "final paycheck" even though it is not for the full amount due would exempt him from paying any remaining balance and leaving me uneligible to appeal to anyone. I have a feeling he is attempting to intimidate me but I don't know the law and had a friend suggest I try asking on here.

Nope, you do not give up any rights to pursue further compensation due you under the law just because you cash the check you have in hand.

I don't actually have the paycheck in hand. It was due last week and when I wrote an email to complain he sent an email back stating he was sending what he felt I deserved rather than what was due and he was putting "final payment - no further negotiations" in the memo and said if I signed it and cashed it then he would no longer be liable for any further payments so I can either cash the check or "take my chances" that the law would favor me. He said the law always favors the employer and that the burden was on me to prove he acted with "malice" and I would more than likely lose all my pay if I contested it and couldn't prove beyond a doubt that he acted in bad will. I am sorry to write so many questions. As I mentioned I feel like he is lying and trying to intimidate me but don't know the law very well.

Whatever. You still don't give up your rights to file a claim with the TWC. However, if what you have IS an enforceable contract (and I'm not at all convinced that it is), it's possible you MAY give up your rights for recourse if the contract was breached. Again, I suggest you take this document to an attorney for further advice.