Federal Communications Commission Chairman Ajit Pai canceled his scheduled appearance at a major upcoming tech industry trade show after receiving death threats, two agency sources told Recode on Thursday.

It's the second known incident in which Pai's safety may have been at risk, after a bomb threat abruptly forced the chairman to halt his controversial vote to scrap the U.S. government's net neutrality rules in December 2017.

For both Pai and the whole of the FCC, the uptick in security concerns also presents a serious challenge to their ability to discuss critical tech policy issues in public view — without jeopardizing their safety or the safety of others in attendance.

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In this case, the exact nature of the threat, made in advance of Pai's fireside chat at the 2018 International CES, isn't clear. A spokesman for Pai at the FCC, for its part, only said Thursday: "We do not comment on security measures or concerns."

But sources at the agency said that federal law enforcement had intervened in the matter, and other FCC offices are expected to be briefed on the matter. The FBI did not immediately respond to emails seeking comment.

A spokeswoman for the Consumer Technology Association, which puts on the annual Las Vegas-based trade show, also declined to comment. Earlier, though, CTA's leader, Gary Shapiro, told the publication Digital Trends that he did not know why Pai had canceled — but raised the fact that he had recently been "subject to vicious and direct attacks and threats."

For months, Pai has been hounded by his critics, particularly online, who view his vote to repeal net neutrality rules as tantamount to destroying the internet. Pai has lamented in speeches and tweets that he and his family have been mocked, attacked and threatened, in public as well as on Twitter, where Pai himself is active.

By the nature of the job, the chairmanship of the FCC is an especially public role, and threats to its leaders and commissioners aren't exactly new. In 2014, for example, protesters descended on the home of then-Chairman Tom Wheeler, a Democrat, and prevented him from leaving his driveway. Then, too, net neutrality had been the issue at hand.

In the most recent debate, though, tensions have been especially high, driven in no small part by broader frustrations among the public with the Trump administration writ large. If the death threats continue, it is unclear how Pai and his fellow commissioners will proceed.

For now, Democratic Commissioner Mignon Clyburn and Republican Commissioners Michael O'Rielly and Brendan Carr each plan to attend CES. So will Maureen Ohlhausen, the acting leader of their sister agency, the Federal Trade Commission. Ohlhausen had been slated to appear alongside Pai at the annual Vegas event.

—By Tony Romm, Re/code.

CNBC's parent NBCUniversal is an investor in Recode's parent Vox, and the companies have a content-sharing arrangement.