A proposed 2016 ballot law would allow adults 21 and older in Massachusetts to legally possess up to one ounce of cannabis and authorize cannabis retail outlets, alongside cultivation and testing facilities.

According to the Campaign to Regulate Marijuana Like Alcohol, retail cannabis sales would include a 3.75 percent state excise tax in addition to the 6.25 percent sales tax, and local governments would have the option of establishing an additional local sales tax of two percent, while imposing limits on the number of retail outlets within local borders.

The ballot question would allow people to grow a “limited number” of cannabis plants in their homes, and a commission that ballot activists say would be similar to the Alcoholic Beverages Control Commission would regulate the cannabis industry.

“Next year, voters will have the opportunity to end the failed policy of prohibition and replace it with a more sensible system,” campaign director Will Luzier, a former assistant attorney general, said in a statement. “Marijuana is significantly less harmful than alcohol, and our laws should reflect that.”

The proposal faces opposition from Gov. Charlie Baker, Attorney General Maura Healey and Boston Mayor Martin Walsh. In March, Healey said that Washington and Colorado, where voters passed cannabis legalization laws in 2012, have not seen a drop in drug trafficking and saw people from out of state purchase “vast amounts” of the drug to traffic it.

Healey said Colorado Attorney General Cynthia Coffman told her reduced prices on the black market keep underground drug dealers in business.

“Certainly they’ve seen some revenues and that was part of the motivation behind this, but at the end of the day they’re seeing some real problems, particularly with the illegal drug and gun trafficking, because oftentimes guns go along with the drug trafficking there,” Healey said.

Bay State Repeal, another group that has mobilized for a voter referendum on legalizing cannabis, has called for a “strong home-grow provision,” along with moderate taxes and regulations that can drive out illegal sales.

“That has not happened in Colorado, but we want it in Massachusetts, so no cash-cow taxation or giant licensing fee,” Bay State Repeal wrote on its website.

Massachusetts politicians have shown little interest in cannabis legalization, but if Healey certifies the initiative petition and activists gather the required signatures, it will appear on the November 2016 ballot.