President Trump’s new head of the Federal Communications Commission has ordered an investigation of NPR and PBS, with an eye toward unraveling federal funding for all public broadcasting.

“I am concerned that NPR and PBS broadcasts could be violating federal law by airing commercials,” Chairman Brendan Carr wrote on Wednesday to the presidents and chief executives of NPR and PBS, Katherine Maher and Paula A. Kerger, respectively. “In particular, it is possible that NPR and PBS member stations are broadcasting underwriting announcements that cross the line into prohibited commercial advertisements.”

The FCC does not directly regulate the two networks. Instead, it evaluates the actions of roughly 1,500 public broadcasting stations across the country, which hold licenses granted by the FCC for use of public airwaves for radio and television, even in the digital age.