Since May 2011, Republicans have been relying on a little-known procedure to keep the chamber in session, even when it was not really conducting any business -- in order to stop the president from making those recess appointments.
The legal basis comes from a 1993 Department of Justice brief saying the president should act only if the Senate is in official recess more than three days.
So, party leaders had arranged for a single Republican lawmaker to show up every three days and gavel the Senate to order, wait around for a while, gavel it to a close, then leave.
Legal experts have disagreed on both the tactical and timing procedures by the Senate, and whether the president has unilateral authority to override those legislative tactics.
The case to be decided by the high court is Noel Canning v. NLRB (12-1115).