The Montana Legislature enacted the Clean Indoor Air Act in 2005 to protect Montanans from the health hazards of breathing secondhand tobacco smoke. The new law went into effect October 1, 2005. It prohibits the use of tobacco products in all public schools and eliminates smoking in most enclosed public places throughout the state. Under the law, Montanans cannot smoke or use spit tobacco in elementary or secondary public schools or on public school property, including playgrounds, parking lots, administration buildings, athletic facilities, school buses, and dormitories.

With limited exceptions, the law also prohibits smoking in any indoor area, room, or vehicle that the general public is allowed to enter or that serves as a place of work, including:

• Restaurants
• Stores
• Public and private office buildings
• Trains, buses, and other forms of public transportation
• Healthcare facilities
• Auditoriums, arenas, meeting rooms, and other assembly facilities
• Family or group day-care homes
• Adult foster care homes
• Buildings that house community colleges and the state university system

Managers or proprietors of enclosed public places are required to post conspicuous signs at all entrances indicating that smoking is prohibited. Bars and casinos may apply for a temporary exception to the law, giving them until October 1, 2009, to comply. Even with an exception, bars and casinos must agree to keep minors out of designated smoking areas and prevent smoke from drifting into non-smoking areas.