When the Senate was on a holiday recess last year, President Barack Obama appointed three new members of the National Labor Relations Board. Upon being brought to the U.S. Court of Appeals for the District of Columbia, a three-judge panel found that Obama’s appointing was unconstitutional. According to Chief Judge David B. Sentelle, the president shouldn't indulge in “free rein to appoint his desired nominees at any time he pleases, whether that time be a weekend, lunch, or even when the Senate is in session and he is merely displeased with its inaction.”
Whether or not the Constitution allows for the president to make recess appointments is a gray area. It is allowed and has been utilized in the past. For example, former president George W. Bush made a recess appointment for United Nations Ambassador John Bolton. However, the numbers of days allowed to pass for an absent Senate before the president is allowed to make an appointment is not defined. While the Senate was on break, pro forma sessions were still being held, which was the basis of the appeals court's decision to invalidate the president’s appointments.
With this case, the Supreme Court would have to look into other board choices made by the president and have the opportunity to finalize a precedent for the law's gray area, assuming the highest court agrees to hear the case. Questions have been raised on the nature of pro forma meetings being used to purposely block appointments to keep the Senate (theoretically) during breaks. It is a tactic that has been used by both Republicans and Democrats. Furthermore, the Supreme Court would have to look into past governmental appointments overall, as the appeals court decision suggests that several past rulings are on grounds for invalidation.