Seth Stern, the director of advocacy at Freedom of the Press Foundation, said he believed Mr. Carr seemed to be setting up a legal pretext for interfering with public media.

“The end of Mr. Carr’s letter tellingly goes far beyond underwriting and talks about his thoughts on whether public media should be funded at all and notes that this underwriting issue might be relevant to a broader legislative debate,” Mr. Stern said. “That was troubling to read.”