Mo. Rev. Stat. § 290.100: Thirty days' notice of reduction of wages, how.

Any railway, mining, express, telegraph, manufacturing or other company or corporation doing business in this state, and desiring to reduce the wages of its employees, or any of them, shall give to the employees to be affected thereby thirty days' notice thereof. Such notice may be given by posting a written or printed handbill, specifying the class of employees whose wages are to be reduced and the amount of the reduction, in a conspicuous place in or about the shops, station, office, depot or other place where said employees may be at work, or by mailing each employee a copy of said notice or handbill, and such company or corporation violating any of the provisions of this section shall forfeit and pay each party affected thereby the sum of fifty dollars, to be recovered by civil action in the name of the injured party, with costs, before any court of competent jurisdiction.