For most of President Obama’s first term, Republicans used legislative trickery to try to prevent the functioning of two federal agencies they hate, the National Labor Relations Board and the Consumer Financial Protection Bureau. First they would filibuster the president’s nominees to the agencies, knowing that neither agency could operate without board members or a director. Then they would create fake legislative sessions for the Senate during its recess, intended solely to prevent Mr. Obama from making recess appointments as an end run.

Astonishingly, a federal appeals court upheld this strategy on Friday. Mr. Obama had declared that Congress was not really open for business during its one-minute, lights-on-lights-off sessions intended only to thwart him, and he made recess appointments. A three-judge panel of the United States Court of Appeals for the District of Columbia Circuit said his N.L.R.B. appointments were unconstitutional, buying the argument of Republicans that the Senate was really in session.

The court even broke with the presidential practice of 150 years by ruling that only vacancies arising during a narrow recess period qualify for recess appointments.

White House officials said the administration would appeal the decision to the Supreme Court, but if it is upheld, it will invalidate scores of decisions made by the labor board over the last year. Without lawfully appointed members, the board would lack a quorum and could take no action, unable to police union elections or ensure that companies treat unions properly. That is exactly the outcome hoped for by business interests and the right, furious that a board under Democratic control tends to rule in labor’s favor (after years of ruling for business during the Bush years).