A Republican lawmaker made a subtle "birther" jab at President Obama during a speech at the Conservative Political Action Conference (CPAC).

Rep. Raúl Labrador (R-Idaho), a freshman member of Congress who was born in Puerto Rico, joked that he had a birth certificate to prove his American heritage.

"I am fortunate to be born American, and I have the birth certificate to prove it," Labrador said at a speech at the opening session of this weekend's conservative gathering in Washington.

The joke is an allusion to some critics' suspicion that Obama was not actually born in the United States, and thus, under the U.S. Constitution, is not legally eligible to be president. Obama has produced a copy of his birth certificate showing he was born in Hawaii, a U.S. state.

Most Republicans have been largely reluctant to question Obama's birth status. Speaker John Boehner (R-Ohio) has said he doesn't doubt Obama.

Still, last Congress, several Republicans sponsored legislation meant to force presidential candidates to produce a legal copy of their birth certificate — a move interpreted as a bow to birthers.