The National Republican Congress Commission (NRCC), in charge of organizing the mid-term elections campaign in the House of Representatives, was hacked in April, the Politico website reported on Tuesday.
This piracy has resulted in the revelation of several thousand sensitive emails, adds the site.
The accounts of four advisers of the NRCC were compromised during computer intrusions detected in April, continues Politico quoting three senior officials of the Republican Party whose identity has not been revealed.
The alert was given by a commission service provider who also notified the company responsible for ensuring computer security of the NRCC.
An internal investigation was opened and the FBI was informed of the situation.
Speaker of the Representatives House Paul Ryan and Republican Majority Leader Kevin McCarthy were only informed once contacted by the news site.
NRCC officials told Politico that they did not want to reveal the piracy immediately so as not to hinder the investigation.