Maybe they can actually make a case out of that, if the checkpoint you are referring to isn't in New Hampshire, or the federal agents file federal charges.
Under the NH Constitution judges have found that drug evidence found at Border Patrol checkpoints was illegally obtained, and cannot be used in state courts.
There is nothing wrong with checkpoints in appropriate locations. I've seen them working very effectively in California. But in New England if you want to catch illegal aliens you head for where they are. And that isn't along the road in northern New Hampshire.
Your information reminds me why my people left effete New England a long time ago.