The committee cited reports of sexual and other misconduct by the Florida Republican in a statement Friday.
The news comes as Gaetz has retained two prominent New York attorneys as he faces a Justice Department investigation into sex trafficking allegations involving underage girls.
The House panel's bipartisan probe is one of the first official indications Gaetz's party leaders are willing to scrutinize his actions
A Gaetz spokesperson said in a statement Friday that Marc Mukasey and Isabelle Kirshner will lead the Republican congressman's legal team. The statement says Gaetz will "fight back against the unfounded allegations against him."
Gaetz has not been charged with a crime and has denied any wrongdoing. He also refused to resign -- or even lay low -- amid mounting political pressure.
Instead, he apparently hopes to solidify his place as one of the brightest stars of the Republican Party's most conservative wing.
During a high-profile appearance Friday night at former President Donald Trump's Doral golf club in Miami, he vowed, "I have not yet begun to fight."
Associated Press reporters Eric Tucker, Michael Balsamo, Will Weissert and Lisa Mascaro contributed to this report.