Mo. Rev. Stat. § 407.928: Restrictions on sales of individual packs of cigarettes.

No person or entity shall sell individual packs of cigarettes or smokeless tobacco products unless such packs satisfy one of the following conditions prior to the time of sale:

(1) It is sold through a vending machine; or

(2) It is displayed behind the check-out counter or it is within the unobstructed line of sight of the sales clerk or store attendant from the checkout counter.