A bill before the state Senate seeks to make Massachusetts the second U.S. state to outlaw the sale of cigarettes and other tobacco products to people under the age of 21.

The measure scheduled for debate on Thursday would hike the minimum age for purchasing tobacco from 18 to 21 statewide. That same age restriction is already in effect in dozens of cities and towns, including Boston.

If passed, the law would take effect Jan. 1 but would exempt anyone who has already turned 18 by that date.

Retailers caught selling tobacco to minors could face fines of $100 to $300 under the proposal. Supporters hope to discourage more young people from taking up smoking.

Hawaii is currently the only U.S. state with a tobacco purchase age of 21.