US lawmakers have voted down a measure giving President Barack Obama the authority to continue the US military action against Libya.
The vote was 295-123, a majority of 172.
The congressional action has no immediate effect on American involvement but represents a setback for the commander in chief.
The vote marks the first time since 1999 that either chamber has voted against a military operation. The last time was over President Bill Clinton's authority in the Bosnian war.
House Republican leaders pushed for the vote, with rank-and-file members saying the president broke the law by failing to seek congressional approval for the three-month-old war.
Some Democrats accused the Republicans of playing politics with national security.