Holder is scheduled to comment on the matter during a 1 p.m. press conference.
The Associated Press reported Monday evening that the Department of Justice had secretly obtained phone records involving as many as 20 reporters and editors in an effort to find out who leaked confidential information to it.
It was not known if Holder authorized or even knew about the investigation.
Republicans, meanwhile, are calling on him to resign following news of the probe.
"Freedom of the press is an essential right in a free society," RNC Chairman Reince Priebus said in a statement.
"The First Amendment doesn’t request the federal government to respect it; it demands it," Priebus said. "Attorney General Eric Holder, in permitting the Justice Department to issue secret subpoenas to spy on Associated Press reporters, has trampled on the First Amendment and failed in his sworn duty to uphold the Constitution."
Read more: http://www.foxnews.com/politics/2013/05/...z2THtoyG4g