A simple Google search gave me this as the top answer to whether or not a DUI checkpoint is legal in MA: https://www.massdefense.com/what-are-your-rights-at-a-dui-checkpoint/#:~:text=Like%20it%20or%20not%2C%20sobriety,as%20well%20as%20interview%20you.

It's legal. People might not like it and I'd argue it's a chance for cops to be unnecessary dickheads, but it's 100% legal and it's asinine to pretend it isn't. I can't believe you demanded a source for something so inherently easy to look up and then call folks a bootlicker for being incredulous that you think such a common practice is illegal.