Massachusetts Attorney General's office announced that any firearm that is a copy or duplicate of already banned rifles are banned. For a rifle to be a copy/duplicate, it has to have essentially same operating system as ARs and AKs, or the components are interchangable with those of a banned rifles.
Current owners of the rifles are not going to be affected.
This is being described as the enforcement of Massachusetts's current law, but similar law in California was struck down several years ago.
Here's the announcement
Boston Globe article