(a) An agreement under this subchapter supersedes a previous statute concerning wages, salaries, rates of pay, hours of employment, or other terms and conditions of employment to the extent of any conflict with the statute.
(b) An agreement under this subchapter preempts any contrary executive order, local ordinance, or rule adopted by this state or a political subdivision or agent of this state, including a personnel board, a civil service commission, or a municipality.

(c) An agreement under this subchapter may not diminish or qualify any right, benefit, or privilege of an employee under this chapter or other law unless approved by a majority vote by secret ballot of the members of the association recognized under § 142.155 at which only members of the association who are eligible to sign a petition under § 142.155 may vote.