Today SCOTUS heard arguments on NLRB v. Noel Canning, regarding when the President can make so-called recess appointments to fill vacancies in Executive Branch positions that require Senate confirmation, without Senate confirmation.
This is allowed by Art. II, Sec. 2, which reads in pertinent part "The President shall have Power to fill up all Vacancies that may happen during the Recess of the Senate, by granting Commissions which shall expire at the End of their next Session."
To me, this boils down to two questions, which are when is the Senate in "recess," and, once determined, does the power apply only to vacancies that arise when the Senate is in recess or vacancies that exist at the time of recess no matter when they arose.
It seems that the answer to the latter question is that the text is fairly clear, POTUS can fill vacancies that happen "during" the recess of the Senate. If they happen when the Senate is in session, too bad. The counter-argument is that there is a longstanding practice to the contrary ("any vacancy will do"), but that doesn't seem persuasive enough to override the text.
The issue then becomes, when is the Senate in recess, other than between the two sessions? Like most things, the Constitution doesn't provide a clear answer. It does state that the Senate "may determine the Rules of its Proceedings." So, perhaps we should ask the Senate whether it was in recess as there is little else to go on in the Constitution and when to start/end sessions seems to fall squarely within the rules of proceedings. The answer from the Senate in this case is that it was not. Case closed, Obama's appointments to the NLRB are invalid, and the NLRB's decisions made without a quorum are simliarly invalid.
I guess the hard question is, given the longstanding practice of making appointments in a manner that is now unconstitutional, do we have to unwind any decision ever made by a recess appointee that did not meet the now more clearly defined procedure? The government raised this issue at argument, but I would expect the Court to either punt by saying that whether such a decision is retroactive to all appointees is not before them, or to just state that their decision applies in this case and all recess appointments made after the date the opinion is published.
I find this interesting because it seems a rare case where Congress punched back at the Executive Branch in a way that really mattered. IIRC, this first took place back when Bush was President and the Senate started holding pro forma sessions to thwart the recess appointment power. If the Senate wins, at it seems it will, then maybe we'll see more of this.