feel (one's) collar

To arrest one (as if by first grabbing them by their collar). The police will feel your collar soon enough if you keep breaking the law. A: "We can't get caught drinking—we're underage!" B: "The cops won't feel our collar, don't worry." Ugh, I have to go down to the police station—seems the cops felt my idiot son's collar last night.

feel someone's collar

arrest or legally apprehend someone.

The image here is of using a person's collar as a means of getting a secure grip on them.