I have worked for the past several years in a medical office in TX as an exempt/salaried employee. I recently became pregnant and gave my employer 2 weeks notice. Prior to giving notice, I checked with the office manager to confirm that I had used all of my vacation time this year and was provided with a document that reflected I had 0 remaining vacation days. On the day before my last day of work, my employer asked me to stay for 2 additional weeks. I explained I could not do this. Later the same day, the office manager came to see me and told me that because I had used my full amount of vacation time, I would not be paid for the last week that I had worked. She is claiming that is company policy. In the past 3 years, I have not heard of any such policy. Can they legally do this? Would TWC do anything for me here?

You must be paid for the days you worked. If you worked 4 days in a workweek, you are owed 4/5 of your weekly salary (since you've used up your vacation).

You can file a claim for unpaid wages with the Texas Workforce Commission.