A fight is heating up in Massachusetts over what could become one of the nation’s strictest rent-control measures.

A group of housing advocates and labor unions want to stop landlords from raising rents by more than the state’s annual rate of inflation—but no higher than 5%—a year. They amassed enough signatures late last year to qualify their proposal for this November’s ballot, launching New England’s most populous state headlong into the debate over whether policing rent helps tenants.

The ballot measure has garnered early polling support in a state with some of the nation’s priciest real estate. The average two-bedroom apartment in Massachusetts goes for about $2,560 a month, 74% above the national average, according to Zillow. In Boston, where such units fetch about $3,370, Mayor Michelle Wu, a Democrat, is supporting the measure.

Opposition is mounting, too. Gov. Maura Healey—also a Democrat—has said she would vote against the measure on concerns that rent control stifles housing production.