Tex. Local Government Code § 143.027

(a) A person appointed to a beginning position in the fire or police department must serve a probationary period of one year beginning on that person's date of employment as a fire fighter, police officer, or academy trainee. In a municipality with a population of less than 1.9 million, the commission by rule may extend the probationary period by not more than six months for a person who:

(1) is not employed by a department in which a collective bargaining agreement or a meet-and-confer agreement currently exists or previously existed; and

(2) is required to attend a basic training academy for initial certification by the Texas Commission on Fire Protection or the Texas Commission on Law Enforcement.

(b) During a fire fighter's or police officer's probationary period, the department head shall discharge the person and remove the person from the payroll if the person's appointment was not regular or was not made in accordance with this chapter or the commission rules.

(c) During a fire fighter's or police officer's probationary period, the person may not be prohibited from joining or required to join an employee organization. Joining or not joining an employee organization is not a ground for retaining or not retaining a fire fighter or police officer serving a probationary period.

(d) A fire fighter or police officer who was appointed in substantial compliance with this chapter and who serves the entire probationary period automatically becomes a full-fledged civil service employee and has full civil service protection.