Workplace smoking laws apply to workplaces with more than five employees. Exceptions include designated lobby areas, meeting and banquet rooms when food is not being served, warehouses over 100,000 sq. ft. with fewer than 20 employees, and truck cabs if no nonsmoking employees are present.
An employer may not knowingly or intentionally permit smoking in any enclosed workplace and must take reasonable steps to prevent nonemployees from smoking. An employer may also designate an entire site as nonsmoking. Smoking is permitted in break rooms designated for smokers.
In California, smoking areas must be in a nonwork area. No employee may be required to enter that room as part of their job (this does not apply to custodial work when the room is unoccupied). The air must be exhausted directly outside with a fan and cannot recirculate to other areas of the building.
In California, if there is a break room for smokers, there must be enough break rooms for all nonsmokers.
For smokers, there are no required accommodations. However, employers with five or fewer employees may permit smoking in a designated area if the following conditions are met:
California 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 California, employers are generally free to adopt policies on smoking in the workplace if they choose to.
An employer may not discharge or discriminate against an employee for engaging in lawful activity during nonwork hours away from the employer's premises.
If you want to go right to the source and look up California 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 Cal. Lab. Code Sections 96, 98.6, 6404.5.