In a case freighted with major constitutional implications, a federal appeals court on Friday overturned President Obama’s controversial recess appointments from last year, ruling he abused his powers and acted when the Senate was not actually in a recess.

The three-judge panel’s ruling is a major blow to Mr. Obama. The judges ruled that the appointments he made to the National Labor Relations Board are illegal, and the board no longer has a quorum to operate.

But the ruling has even broader constitutional significance, with the judges arguing that the president’s recess appointment powers don’t apply to “intrasession” appointments — those made when Congress has left town for a few days or weeks.

The judges signaled the power only applies after Congress has adjourned a session permanently, which in modern times usually means only at the end of a year. If the ruling withstands Supreme Court scrutiny, it would dramatically constrain presidents in the future.

And the court ruled that the only vacancies that the president can use his powers on are ones that arise when the Senate is in one of those end-of-session breaks. That would all but eliminate the list of positions the president could fill with his recess powers.

But the court said in the ruling that its duty was not to speed up government, but to hold to constitutional principles.

“If some administrative inefficiency results from our construction of the original meaning of the Constitution, that does not empower us to change what the Constitution commands,” the judges wrote.

Divining the founders’ intent

Presidents of both parties have used the controversial power in recent decades, but the three-judge panel said they concluded that that was not what the founders intended that.

“The dearth of intra-session appointments in the years and decades following the ratification of the Constitution speaks far more impressively than the history of recent presidential exercise of a supposed power to make such appointments,” the judges wrote. “Recent presidents are doing no more than interpreting the Constitution. While we recognize that all branches of government must of necessity exercise their understanding of the Constitution in order to perform their duties faithfully thereto, ultimately it is our role to discern the authoritative meaning of the supreme law.”

The judges said the recess power was created for a time when Congress met only a few months out of the year, and was designed for the president to fill vacancies during the long periods when Congress was out. In modern times, when Congress is almost always capable of meeting, the recess powers should be more circumscribed.

The NLRB said it was not yet ready to respond to the ruling Friday morning, and the Justice Department didn’t respond to a request for comment.

The case is likely to end up before the Supreme Court, and it turns on the definition of what the Constitution means when it says “recess.”

Last January Mr. Obama named union lawyer Richard Griffin and Labor Department official Sharon Block, both Democrats, and a Republican, NLRB lawyer Terence Flynn, to the labor board using his recess powers. He also named Richard Cordray to head the new Consumer Financial Protection Bureau, using those same powers. The Cordray appointment was not part of the court case decided Friday, but has been challenged separately in another suit.

Noel Canning, a bottling company, sued the NLRB, arguing that a rule issued by the new board was illegal since the recess appointments were unconstitutional. Senate Republicans, led by Minority Leader Mitch McConnell, joined in the suit.

Skeptical questioning

The appeals court panel, which sits in Washington, D.C., was skeptical of Mr. Obama’s case during oral argument in early December, with Chief Judge David B. Sentelle and Judge Thomas B. Griffith peppering the administration lawyers with questions.

The Constitution gives the president the power to nominate judges and executive branch officials, but the Senate must vote to confirm them before they take office. Article II, Section 2 of the Constitution grants the president powers “to fill up all vacancies that may happen during the recess of the Senate.”

Those powers have produced centuries of give-and-take, with senators regularly slow-walking nominees and the White House looking for ways to get its nominees in place — including the recess appointment.

Mr. Obama’s move, though, appeared to break new ground by acting at a time when the Senate was meeting every third day — specifically to deny him the chance to make recess appointments.

The problem is the word “recess” has several meanings in legislative-speak. It can mean a short break during the day, it can mean a break of days or weeks for a holiday, or it can mean the end of a yearly session.

The president argued that even though the Senate was convening every three days, the pro forma sessions didn’t allow any business, and nearly every senator was absent from the chamber, signaling that the Senate wasn’t able to perform its confirmation duties and should be considered essentially in recess.

His opponents had warned that if Mr. Obama’s stance prevailed, then presidents could make appointments when the Senate takes its recess for weekly party caucus lunches.

The judges on Friday ruled that the only clear bright line is when the Senate recesses at the end of the year.

Victor K. Williams, an assistant professor at Catholic University School of Law who filed briefs arguing that the court should reject the case as a political question between Congress and the president, called the judges’ ruling “historically wrong.”

“This panel of the D.C. circuit has accomplished what Minority Leader Mitch McConnell failed to do. Minority Leader McConnell said that his No. 1 objective was defeating Barack Obama and Barack Obama’s attempt to govern. This D.C. circuit panel has been successful where McConnell failed. They have really, effectively challenged the president’s ability to govern,” Mr. Williams said.

The judges’ ruling puts them at odds with several other federal appeals courts that have ruled the other way. And another case is making its way through the D.C. circuit and could be heard by another three-judge panel.

Mr. Williams said the Justice Department faces an interesting choice: It could allow those other cases to work their way through the rest of the courts, or it could appeal immediately to the Supreme Court.

The administration could also ask the full D.C. circuit to re-hear the case.