It also depends on what they were trying to get you to sign. For instance if they were saying that you must sign a write up admitting you were not discriminated against (when you were) then that would be a reason to sue. You should go see a local employment lawyer and get some advice. It could also be that they were trying to force you to sign a write up that was false because they want to justify your future termination for an illegal reason -- like age. So my answer is simply that while Texas is an at-will state if the attempt to have you admit something that was false is just an excuse to fire you for a discriminatory reason (for example disability, age, sex ect...) then you may have a case for wrongful termination.
Texas is an employment at will state. Typically, unless an employee has an employment contract, or is employed under a collective bargaining agreement through a union, the employer can modify or terminate the employment at any time with or without cause. If an employer, at any time, decides they no longer want to employ someone, for any non-discriminatory reason, that employee can legally be terminated. However, an employer generally cannot modify or terminate the employment for prohibited discriminatory reasons (such as racial discrimination), or in retaliation for certain protected actions (such as whistle-blowing). The situation you describe does not appear to constitute prohibited discrimination or retaliation.
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