yep! Texas is a right to work state and these morons can be fired for ANY REASON!!!
That's not correct. Even in an employment at will and/or right to work state, you can't fire employees in violation of specific laws. If these employees had put something in their letter about how this actually impacts their terms and conditions of employment, and not just their "values", they'd have probably been protected under Section 8(a)(1) of the NLRA. As it is, there's a good chance they can be fired legally, although they'll probably file an NLRB complaint anyway.