A U.S. appeals court has ruled that President Barack Obama violated the U.S. Constitution when he used recess appointments to fill a labor board.
The court ruled Friday that the Senate was not actually in recess when the president appointed three members to the National Labor Relations Board in January 2012.
The court ruling could jeopardize hundreds of NLRB decisions made over the past year, including some that have made it easier for unions to organize.
Mr. Obama has said his appointments were appropriate because the Senate was on a holiday recess.
Republicans have said the Senate had not formally adjourned, even though most of its members were out of town. They say the president wanted to undercut the Senate's power to confirm nominees.
The appeals court ruled the Senate had technically remained open in pro forma sessions, in which a lone member can gavel in and then immediately gavel out. The court said the pro forma sessions were valid. The White House has argued the pro forma sessions were a sham.
White House spokesman Jay Carney denounced the court's decision Friday as "novel and unprecedented." He said the ruling "contradicts 150 years of practice by Democratic and Republican administrations."
The case has been seen as a test of the president's ability to bypass the confirmation process in the Senate, whose members have the constitutionally enshrined power to block nominees.
Legal experts expect the White House will challenge the ruling rendered by judges appointed by Republican presidents, and the case could go to the Supreme Court. President Obama is a Democrat.
The ruling also throws into question the legitimacy of President Obama's recess appointment of Richard Cordray to head the Consumer Financial Protection Bureau. Cordray's appointment, made at the same time as the NLRB appointments, has been challenged in a separate case.