WASHINGTON (Reuters) - The U.S. Federal Communications Commission’s chairman said Tuesday the agency does not have authority to revoke broadcast licenses, despite suggestions from President Donald Trump.

Ajit Pai, Chairman of the Federal Communications Commission, testifies before a Senate Appropriations Financial Services and General Government Subcommittee on Capitol Hill in Washington, U.S., June 20, 2017. REUTERS/Aaron P. Bernstein

Ajit Pai, a Republican who was named chairman of the telecommunications regulator in January, broke days of silence by rejecting Trump’s tweet that the FCC could challenge the license of NBC after stories Trump declared were not true.

“Under the law, the FCC does not have the authority to revoke a license of a broadcast station based on the content,” Pai said at a forum. “The FCC under my leadership will stand for the First Amendment.”

The First Amendment of the U.S. Constitution guarantees freedom of speech and freedom of the press.

Democrats had been pushing Pai to denounce Trump’s suggestion that broadcast licenses could be threatened following reports by NBC News that his secretary of state, Rex Tillerson, had called him a “moron” after a discussion of the U.S. nuclear arsenal.

“With all of the Fake News coming out of NBC and the Networks, at what point is it appropriate to challenge their License? Bad for country!” Trump tweeted on Wednesday.

Trump and his supporters have repeatedly used the term “fake news” to cast doubt on media reports critical of his administration, often without providing any evidence to support their case that the reports were untrue.

Any move to challenge media companies’ licenses, however, would likely face significant hurdles.

The FCC, an independent federal agency, does not license broadcast networks, but issues them to individual broadcast stations that are renewed on a staggered basis for eight-year periods.

Comcast Corp, which owns NBC Universal, also owns 11 broadcast stations, including outlets in New York, Washington, Los Angeles, San Francisco, Boston, Dallas and Chicago.

When reviewing licenses the FCC must determine if a renewal is in the public interest. Courts have held that a station exercising its First Amendment rights is not adequate grounds to challenge a license.

The agency does not issue similar licenses for cable networks such as CNN and MSNBC, or regulate internet news or other websites.

In the early 1970s, then-President Richard Nixon and his top aides discussed using the FCC’s license renewal process as a way of punishing The Washington Post for its coverage of the Watergate burglary that ultimately brought down his presidency.