Many of Mr. Olbermann's fans responded to the decision by accusing Comcast, the incoming owner of NBC Universal, of forcing him out for political reasons. Several of Comcast's top executives have been financial supporters of Republicans; Mr. Olbermann is largely credited with establishing MSNBC's liberal voice.

Comcast issued an official statement Friday denying any involvement in the decision, saying it had no operational control of the company yet, and adding: "We pledged from the day the deal was announced that we would not interfere with NBC Universal's news operations. We have not and we will not."

But the company is still drawing criticism for the move. Marvin Ammori, a law professor at the University of Nebraska, said in an e-mail Friday, "Keith Olbermann's announcement tonight, the very same week that the government blessed the Comcast-NBC merger, raises serious concern for anyone who cares about free speech. Comcast proved expert in shaking down the government to approve its merger. Comcast's shakedown of NBC has just begun." Professor Ammori is a former adviser to the nonprofit group Free Press, which opposed the Comcast-NBC deal.