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Congressional Republicans and business groups that supported the lawsuit said the result represented a needed check to an agency they have long accused of tilting strongly toward unions under Mr. Obama.

“The Obama administration has consistently used the NLRB to impose regulations that hurt our economy by fostering uncertainty in the workplace and telling businesses where they can and cannot create jobs,” GOP House Speaker John Boehner, who filed a brief supporting the challenge to the board’s legitimacy.

Dennis Devaney, another former NLRB board member first appointed to the board by President Reagan, cheered the court’s ruling.

“I think the court got it right,” Mr. Devaney said. “This was bad public policy by the Obama administration. It was a mistake. It’s good to see that the court agrees they were unlawful appointments.”

But the labor movement joined with the White House in taking strong issue with the ruling.

AFL-CIO chief Richard Trumka denounced the decision as “shocking” and said the NLRB members should stay at their posts as the legal battle proceeds.

“We fully expect this radical decision to be reversed, and that other courts addressing this issue will uphold the president’s recess appointment authority,” Mr. Trumka said in a statement. “In the meantime, the appointees to the National Labor Relations Board remain in their jobs and the NLRB remains open for business.”