Employers may *not* retaliate against an employee for filing wage and hour claims. Since, however, any lawsuit for $18k must be taken seriously--and since also, if they attempt to retaliate against you illegally, that itself may give you grounds to sue them--IF you are actually sued, you should retain a lawyer to both defend you and pursue counterclaims. On the other hand, if you are not actually sued--e.g. it's just bluster--there's no need to contact an attorney. In either case though, it would be a good idea to contact the TX Labor Dept., make them aware of the threat, and provide a copy of the letter to them as evidence. Good  luck.