Can my employer punish me for giving money to a coworker for covering my shift?

r/

Location: Texas & Entire United States

My employer has begun punishing and threatening termination to employees who offer monetary incentives to other employees for working their shifts. We have a system that allows us to trade and drop shifts to other employees. So the physical giving up a shift is allowed, but giving a cash gift to each other for taking a shift is what is being punished. Is this legal?