Workplace smoking laws apply to enclosed indoor workplaces. Exceptions include bars or restaurants seating fewer than 50 people, bowling alleys and billiard parlors, and stadiums seating more than 15,000 people.
Smoking is prohibited throughout the entire workplace except for designated smoking areas. Smoking is permitted in designated smoking areas (may not be more than 30% of the workplace).
In Missouri, smoking areas must have existing physical barriers and ventilation systems that isolate the area.
Missouri doesn’t specifically require employers to provide workplace accommodations for nonsmoker employees.
Missouri laws don’t address employer policies on smoking in the workplace. Local laws regulating smoking -- at the city, county, or town level -- may require employers to have a policy on smoking in some areas. And even though it’s not required by law in Missouri, employers are generally free to adopt policies on smoking in the workplace if they choose to.
An employer may not refuse to hire, discharge, or in any way discriminate against an employee for lawful use of tobacco offsite during nonwork hours, unless use interferes with employee's or coworkers' performance or employer's business operations.
If you want to go right to the source and look up Missouri law on workplace smoking laws -- or if you're writing a letter to your employer or employee and want to cite the applicable law -- the relevant statute(s) can be found at Mo. Rev. Stat. Sections 191.765 to 191.771, 290.145. Workplace smoking information is also available in Nolo's books Your Rights in the Workplace, by Barbara Repa (Nolo) and The Employer's Legal Handbook, by Fred Steingold (Nolo).