Penalty box
The #MLAlienation account posted a run of interesting possibilities for dealing with departments that mistreat adjuncts and, more generally, supporting adjuncts within the Association as a whole, including this:
#MLA16 “They could refuse to allow departments whose PTF earn less than XX to interview at their convention.”
— MLAlienation (@MLAlienation) December 26, 2015
I'd previously had thoughts along these lines on a different topic, but pondering it a bit more, there is at least one major problem in the way of enforcing such a rule: "departments" don't interview at the conjunction; members of departments do. That is, "the Department of English, College at Brockport, SUNY" doesn't reserve a suite, but "Current Department Chair" does. There's no way to ban the department--just people from the department. Which is the rub, because barring some easily-outmaneuvered question on the registration form ("Are you coming to the conference to interview? To deliver a paper? To spend all your time in the book exhibit?"), the only way to disallow departments from interviewing at the convention is to disallow anyone associated with said department from attending in the first place. And while that is probably something a computer could handle easily enough, it would disadvantage graduate students, adjuncts, and anyone else in the department who might be in need of a job. (More cynically, I can imagine a lot of universities that might shrug at the news that their department was banned from the MLA. Saves money, and all that.)
Now, that being said, it's certainly within the MLA's power to name-and-shame universities that don't pay their part-time faculty a living wage. It would take some work (complaining that a Directional State in a low COL rural area isn't paying the same as a university in New York City makes little sense, for starters), but it would certainly be doable. It might also be possible for the MLA to establish a minimum payment threshold below which a department couldn't advertise in the JIL--denying them an imprimatur, in other words--but that would probably cause more trouble for jobseekers than the department.