A senior House Republican has served a top FBI official with a subpoena for all the material from the bureau's investigation into Hillary Clinton's use of a private email server.
Chaffetz said his committee shouldn't have to issue a subpoena to see unclassified information. Republicans have said the documents "did not constitute a complete investigative file" as numerous records had been substantially blacked out or were missing.
"Where in the Constitution does it say that I can't see that?"
FBI Director James Comey last week defended the decision to forgo criminal charges against Clinton after a lengthy probe into whether then-Secretary of State Clinton mishandled classified information that flowed through the private email system located in her NY home.
Republican investigators panned his decision and are holding a series of hearings on Mrs. Clinton's decisions and the related probe.
"We decide what's relevant - not the Department of Justice, not the FBI", Chaffetz said.
During a hearing about the classifications and redacted information in the FBI report on the investigation of Hillary Clinton's email server released ahead of the Labor Day weekend, the FBI's Acting Assistant Director for Congressional Affairs Jason Herring said he could not commit to turning over unredacted documents.
When Herring accepted the subpoena, Chaffetz delivered the formal line that traditionally accompanies such a service.
Comey announced in July that he had recommended against criminal charges for Clinton.
Ranking member Elijah E. Cummings, Maryland Democrat, said the committee should have kept Monday's discussion behind closed doors to avoid the accidental disclosure of classified information.
Earlier in August, the Federal Bureau of Investigation determined not to prosecute Clinton for her use of private email account during her service as secretary of state.
Recent polls show her lead over GOP rival Donald Trump is shrinking, and she didn't immediately disclose a pneumonia diagnosis that's forced her to take a break from the campaign trail. Over Democratic protests, Chaffetz has scheduled another hearing for Tuesday to question computer technicians who worked on Clinton's e-mail system. Doing otherwise, he said, would risk "a chilling effect" that might discourage witnesses from cooperating with investigations.
The FBI provided portions of the Clinton probe file to Congress last month and warned lawmakers that the documents "contain classified and other sensitive material" and are not to be made public.