Sources close to Arianna Huffington are claiming just that.
Arianna Huffington is currently on book tour for her new political tome Right Is Wrong: How The Lunatic Fringe Hijacked America, Shredded The Constitution, And Made Us All Less Safe, in which she goes after Tim Russert (and justifiably so). 
She's booked all over CNN, ABC, and CBS (but not Fox News Channel because she chose not to go on there).
And NBC?
Well, one insider says she was booked on Keith Olberman and Morning Joe to talk about her tome -- and then unbooked.
"These are shows that call her regularly to come on. And then the word came from on high that she had to be cancelled."
Arianna's accolytes are pointing the finger at Tim Russert, well known to be ridiculously thin-skinned, for blackballing her internally at NBC and not permitting her on any of the NBC network or cable outlets.
It's certainly possible, considering how much clout the Washington bureau chief wields at the company (not to mention how much profit his Meet The Press yields for the company).
NBC did confirm to me that Arianna Huffington won't be booked on any of the NBC network or cable shows past or present or future for her book.
(Interestingly, a Knopf source says the publisher was never given a definitive no. "We were just told to 'Call back tomorrow.' There was never any explanation.")
Granted Right Is Wrong is only #209 on Amazon.com, but Huffington pals are arguing to NBC it's a big book tour by a big name. "We get pitched countless books, and most of them don't make it on the air. And this one didn't," the network news spokesperson told me.
The spokesperson points out that Huffington has had nasty things to say about Russert "for years" through HuffPo's RussertWatch but she's still been booked on NBC shows. "Arianna must be dialing for dollars again," the spokesperson snarked.
Meanwhile, the respected Columbia Journalism Review just announced it will pick up HuffPo's RussertWatch as a regular online feature.
So what does Huffington say about Russert in her tome?
-- Russert's July 1, 2007, Meet The Press interview with Homeland Security Secretary Michael Chertoff "was about as priapic a display as you're ever likely to see outside of a porno film or the monkey cage at the zoo, with Russert desperately trying to get Chertoff to pump up the panic meter..."
-- Russert's Meet The Press has been the Bush-Cheney "administration's top choice for push-back as its lies about Iraq were unraveling, because the White House could 'control' the message more easily there."
-- Russert is "one of the temple guards of conventional wisdom" and "a conventional wisdom zombie".
-- A 7-page scathing analysis of Russert and Meet The Press, based on this premise: "The reason the conventional wisdom survives no matter how many times its lies are exposed is that shows like Meet The Press allow their guests to go unchallenged."
