Earlier on "Imus in the Morning," Don Imus announced, "Lou Dobbs, the grassy knoll nut from CNN, was supposed to be on this morning, but he called up and canceled because apparently somebody there at CNN and over at MSNBC won't let any of their people appear with me anymore because -- well, we know why."

The NY Observer's Felix Gillette wants to know if there is a CNN and MSNBC ban on talent appearing on Imus' show, which is now simulcast on Fox Business Network.

Have MSNBC and CNN executives, in fact, implemented such a policy?

An MSNBC spokesperson declined to comment. But a source at the network told The Observer that Imus viewers are unlikely to see anyone from MSNBC on the show anytime soon, if ever.

As for Mr. Dobbs' absence on Imus today, a CNN spokesperson confirmed that the network did not give approval for the booking, eventually resulting in the cancellation.

Earlier this month, Imus mocked CNBC's Charlie Gasparino after he also had to cancel an appearance.