Recess appointments were upheld by the SCOTUS. Basically, The question was whether pro-forma sessions were actually recess or not. They ruled that they were.
So in essence, any majority party that is willing to stay in session at all times can block appointments. That has its perils.
If you read the actual ruling, they affirmed the Presidential power of recess appointments.
"The Court began with the first question presented in the case: whether the Constitution allows the president to make recess appointments during intra-session recesses (breaks that occur within the two one-year sessions between congressional elections) or only during inter-session recess (the break between the two one-year sessions). Its answer on this question is a victory for the Obama administration and future presidents who want to be able to make recess appointments. Again relying heavily on a long tradition of recess appointments, it concluded that the constitutionality of a recess appointment does not hinge on whether it is made during an intra- or inter-session recess. After all, the Court noted, if the purpose of the Recess Appointments Clause is to ensure the continued functioning of the Federal Government when the Senate is away, it doesnt really matter what you call the recess. If the Senate isnt there, it isnt there."
"But theres a catch one that narrows the scope of the ruling. Even if it doesnt matter whether the recess is an intra- or inter-session one, it does matter how long the recess is. Here the Court said that any recess that is shorter than three days is not long enough to make a recess appointment necessary. And a recess that is longer than three days but shorter than ten days will, in the normal case, also be too short to necessitate a recess appointment. (The Court added that there may be very unusual cases such as a national catastrophe . . . that renders the Senate unavailable but calls for an urgent response in which recess appointments would be permitted even though the recess was still shorter than ten days.)
