Mo. Rev. Stat. § 290.530: Law not to interfere with collective bargaining rights.

Nothing in sections 290.500 to 290.530 shall be deemed to interfere with, impede, or in any way diminish the right of employees to bargain collectively with their employers through representatives of their own choosing in order to establish wages or other conditions of work in excess of the applicable minimum under the provisions of sections 290.500 to 290.530.