The D.C. Circuit says no, the 7th Circuit says yes. For the details, see Ross Runkel’s post, Is 2-Member NLRB authorized to issue orders? Opposite decisions on the same day.
To make matters even more complicated, the 1st Circuit in March held the 2 member decisions were valid, see Two Member NLRB Legal, At Least in the First Circuit.
This kind of circuit split usually ends up in the Supreme Court, but it may also speed up the confirmation process for the Board nominations of Craig Becker and Mark Pearce. Even when they are confirmed, there will still be one vacancy on the five member board.