WASHINGTON (AFP) - A US appeals court dealt a blow Friday to President Barack Obama, ruling that he violated the US Constitution when he made "recess" appointments to fill administration vacancies.

The decision, with which the White House strongly disagreed, focuses on the validity of three appointments to the National Labor Relations Board that were made on January 4, 2012.

But it could have broader implications for presidential power in the appointments process.

It also raises questions about the validity of the appointment of Richard Cordray as head of a consumer watchdog agency which was done on the same day, over intense Republican objections. Cordray's appointment was not part of the legal case decided Friday. A new congressional session had begun the day before the 2012 appointments but, adhering to tradition, the senators left town for the holidays, although they were available to potentially act on appointments if need be.

Obama had argued that his appointments were appropriate because the Senate was in a holiday recess. But the US Court of Appeals for the District of Columbia declared that the Senate had technically remained open in pro forma session, in which a lone member can gavel in and then immediately gavel out.

The White House had consistently claimed such sessions were aimed at retaining the ability to block presidential appointments without Senate approval, but the court said the pro forma sessions were valid. "An interpretation of 'the Recess' that permits the president to decide when the Senate is in recess would demolish the checks and balances inherent in the advice-and-consent requirement," the judges said in their opinion.

Recess, the judges said, "is limited to intersession recesses," and not pro forma sessions when no business occurs. "Considering the text, history, and structure of the Constitution, these appointments were invalid from their inception."

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.

The White House denounced the ruling as "novel and unprecedented." "It contradicts 150 years of practice by Democratic and Republican administrations," press secretary Jay Carney told reporters. Congressional research shows more than 280 intrasession recess appointments by Democratic and Republican administrations dating back to 1867, Carney said.

"That's a long time, and quite a significant precedent." The AFL-CIO, the country's largest labor union federation, blasted the court decision as "shocking," arguing it would deprive both parties of a "critical" governing tool. "We fully expect this radical decision to be reversed, and that other courts addressing this issue will uphold the president's recess appointment authority," AFL-CIO president Richard Trumka said.

But several Republicans hailed the court decision, including House Speaker John Boehner, who welcomed it as "a victory for accountability in government."

Senate Minority Leader Mitch McConnell went straight to one of the contentious political ramifications of the decision.

"This decision now casts serious doubt on whether the president's 'recess' appointment of Richard Cordray to the Consumer Financial Protection Bureau, which the president announced at the same time, is constitutional," McConnell said.

Three weeks after the January 2012 appointments, Chuck Grassley, the ranking Republican on the Senate Judiciary Committee, denounced Obama's move as "an outrageous and unconstitutional power grab," saying the Senate was in fact in session.

On Friday he said the court's decision reaffirms that the Senate's constitutional role in the appointment process is a safeguard "against unchecked government power."