The ruling was a victory for Obama's Republican rivals, who had accused him of trying to slip nominees past lawmakers in order to block the Senate's legal right to oppose them.
The issue had reached the court thanks to a lawsuit filed by the Noel Canning company, which contested the legitimacy of the NLRB appointments after the board ruled against it in a dispute.
"The recess appointments clause eliminates Senate approval in order that the president can ensure the continued functioning of the federal government when the Senate is away," Breyer said. "But it should not give power to the president to avoid Senate approval on a regular basis. We conclude that the phrase 'the recess' includes any recess of 10 or more days, whether it is an intra-session recess or an inter-session recess."
Republicans hailed the ruling.
"For too long, our president has operated by fiat, bypassing Congress and overriding the will of the American people," said Republican Senator John Cornyn. "Today's ruling sends a clear message against President Obama's power grabs and restores more constitutionally required accountability for all nominations going forward."
Copyright Agence France-Presse 2014