Carmen Aristegui said Wednesday that she was let go by MVS radio for refusing to apologize for her comments Friday regarding a congressman's allegation that President Felipe Calderon is an alcoholic.
Aristegui said the accusation was serious and Calderon should respond, though the lawmaker provided no evidence.
Officials from Calderon's office have said such rumors don't merit a response, but late Wednesday the president's personal secretary, Roberto Gil, defended him at a brief news conference where the sole topic was Calderon's busy agenda.
Gil said that in the last year Calderon has attended 1,779 public events, or about seven a day.
"During the four years of his administration, he has never missed any event because of health problems," Gil said. "This work pace is the best proof of his good health, physical strength and integrity."
MVS announced Aristegui's dismissal Monday, saying she violated the station's code of ethics by giving credibility to a rumor.
"An act like this is only imaginable in a dictatorship that nobody wants for Mexico: punishing for opining or questioning rulers," Aristegui said at a news conference.
The firing of a media celebrity, who is ubiquitous on the Mexican airwaves between her morning drive-time radio show and a talk show on the cable TV channel CNN en Espanol, blew up on Twitter and caused a congressional debate.
Aristegui has been honored with top journalism prizes and is known for a direct style of questioning that is unusual in Mexico, a country where media independence is still evolving after 71 years of government control under the Institutional Revolutionary Party, or PRI, which ruled until 2000.
Some journalists say freedom of expression remains an issue because government advertising is a major source of funding for many publications, and thus leverage for influence.
Aristegui claimed Calderon's office called MVS after her show and demanded a public apology. She said the station is under government pressure because it is awaiting approval to renew its radio frequency concession.
MVS did not return a phone call requesting comment Wednesday.
An official from Calderon's office denied it had demanded an apology and insisted it had nothing to do with Aristegui's dismissal. In a statement, the president's office said the federal government has been "scrupulously respectful of freedom of expression" and says it does not mix politics with issues of telecommunications.
"The decision in that area are made with full transparency and strict adherence to the law and without any other consideration," the statement said.
Aristegui, on her program Friday, was discussing lawmaker Gerardo Fernandez Norona, a member of the leftist Labor Party who caused a ruckus in Congress last week when he held up a banner with Calderon's photograph that read: "Would you let a drunk drive your car? No, right? So why would you let him run the country?"
The episode prompted Congress to suspend its session.
Aristegui defended her decision not to apologize.
"Not only am I not retracting myself, and I'm not apologizing because there is nothing to apologize for, but on the contrary, I reiterate that the presidency should comment about this issue," she said.
The Paris-based media advocacy group Reporters Without Borders said MVS's failure to clearly explain its decision "fuels the hypothesis that this is due to political pressure, even censorship."
But some Mexican journalists are not on Aristegui's side.
In a column Tuesday, Ciro Gomez Leyva, editor of the newspaper Milenio, dismissed allegations that Calderon has a drinking problem as unfounded rumors spread by "mediocre Labor Party lawmakers, one or two columnists and malicious tweeters."
Gomez Leyva did not mention Aristegui by name but implicitly criticized her, saying his newspaper would not have written a story on the allegations.
Lawmakers debated the subject Tuesday, with some Labor Party members insisting there must have been government pressure to fire Aristegui.
Leading PRI lawmaker Beatriz Paredes, whose party is struggling to shed its authoritarian image, said Aristegui had become a symbol of the need for a freer media in the country.
"We need criticism, objective criticism, authentic criticism," Paredes said.
Associated Press writer E. Eduardo Castillo contributed to this report.