A group of employers agree not to compete with each other on job offer timing, basically by making all students wait until a certain date to find out if they have a job. Students, who for a variety of reasons may value an early decision / clarity on their job plans are denied this opportunity by the cartel. Who is this?
Well, it could be the NBA, which operates this way, because historically Congress and the courts have cut sports leagues slack on such anti-trust issues. But in this case we are referring to an agreement among Federal judges to restrain competition for law clerks.
As with most all cartels that are not backed up by force of law, the cartel has broken up because there was too much incentive to "cheat". Which is exactly why anti-trust laws are not required, because such cartels always go kaput in a free market. In fact, the only stable cartels in the US have tended to be those that are backed by the force of law and guns.