Howard Stern's words may not carry the same weight now that he's on satellite radio, but he's still got enough juice to get a pesky critic fired. John Mainelli, the New York Post writer who irked Stern by reporting a rumor Tuesday that he would return to terrestrial radio with his tail between his legs, has left the paper after receiving an ultimatum from editor in chief Col Allan.

Allan told Mainelli Wednesday that he had to choose between his freelance job covering the radio industry for the Post and his lucrative sideline consulting for radio stations and owners. "I consider myself fired," Mainelli tells Radar. "I can't live on what I earn from the Post."

Mainelli claims he has made no secret of his consulting relationships in the nearly eight years he's worked at the paper and has always been careful to recuse himself from stories that might present a conflict of interest. But Allan, according to a Post spokesman, was not aware of the arrangement, and would have put a stop to it long ago had he known. Stern has been waging war on Mainelli since Tuesday, when Mainelli reported on speculation that Stern might cut a deal to get part of his broadcast back on terrestrial radio. (Since Stern left CBS in January, his show has only been available to Sirius subscribers.)

Though Mainelli was merely picking up a report from Inside Radio, an industry trade, Stern chose to blast him rather than the source—probably because Mainelli spiced up his story with other damaging details, such as a rumor that Stern was having trouble booking high-profile guests and had lost popularity as an Internet search term. Stern's Howard 100 news team called attention to Mainelli's consulting ties on air, and their reporting was picked up by journalism blog Buzzmachine.com.

Asked whether he's feuded with Stern in the past, Mainelli says, "He's feuded with me," over the number of subscribers Stern has brought to Sirius, among other issues. Nevertheless, Mainelli claims he's been a fan of Stern's—until now.

"I'm very disappointed, and I'm really pissed at Howard Stern," he says. "From now on, anything I write about him will have to have a disclaimer: John Mainelli has an ax to grind against this man."