After labor groups in Missouri collected enough signatures to prevent a right-to-work law from immediately taking effect in the state, both they and their opponents are gearing up for the next step: a referendum on the law that will take place in the November 2018 election. A similar law was rejected by Missouri voters in 1978, in a time when there were far more unionized workers in the state, and when such workers were more heavily concentrated in the private sector.
See "Right to work affects unions most, but all Missouri voters will have a say in 2018", Jo Mannies, St. Louis Public Radio, August 23, 2017