Mo. Rev. Stat. § 393.136
Retroactive operation prohibited.
393.136. Retroactive operation prohibited. — Notwithstanding the foregoing, any such charge which is being made or demanded on November 2, 1976, shall not be deemed unjust or unreasonable by reason of section 393.135 , and shall not be prohibited thereby, for a period of ninety days after the effective date of this law.
(Adopted by Initiative, Proposition No. 1, November 2, 1976)