MEXICO CITY » When Carmen Aristegui, Mexico’s most famous radio personality, was abruptly fired this month, nobody expected her to go quietly. But anger over her dismissal has been rising steadily, and it has turned up the heat in this country’s charged political atmosphere.

Conspiracy theories have abounded since a dispute between Aristegui and her employer, MVS Communications, ended in her departure. She has become an emblem of press freedom under siege, and social media has lighted up with demands for her return to the airwaves.

Even her critics, who point to a lack of reportorial rigor in many of her stories, argue that her dismissal removed one of the few broadcast journalists in Mexico who openly challenge authority. Many journalists contend that Aristegui’s case is part of a broader attempt by the government to check aggressive news coverage.

"Today we have radio that is less plural than it was two weeks ago," said Razl Trejo, a media expert at the National Autonomous University of Mexico. "I have been very critical. But I think her voice is very healthy for Mexican society."

Aristegui leads a team of 17 reporters who uncovered the existence of a mansion in Mexico City’s most exclusive neighborhood, custom-built for President Enrique Peqa Nieto’s wife, Angilica Rivera, by a company that had won hundreds of millions of dollars in government contracts.

Aristegui’s departure "silences a voice," said Ricardo Raphael, a writer who coordinates the journalism program at CIDE, a Mexico City university. "We journalists received the message. Investigative journalism is not well regarded by the government – and even less so if it is used to investigate the conflicts of interest" between the president’s inner circle and private companies.

The Aristegui team’s report on the mansion, which appeared in November, opened a national debate about corruption and conflicts of interest and helped strengthen anticorruption legislation working its way through Congress. The report also put Peqa Nieto’s government further on the defensive; it was already reeling in the face of public anger over the disappearance of 43 rural college students in September, allegedly at the hands of a drug gang and a corrupt mayor.

The president’s popularity and credibility have plummeted since, according to opinion polls.

For decades, Peqa Nieto’s party, the Institutional Revolutionary Party, or PRI, assured itself of a pliant news media through a combination of bribery and threats. Broadcasters and publishers knew that coverage that displeased the government could threaten a valuable concession, cut off newsprint supplies, bring on a tax audit or cost government advertising.

After the PRI lost power in 2000, Mexico’s news media became more freewheeling. But, analysts argue, under Peqa Nieto, the government has been trying to restore some of the old forms of control, using government advertising and its authority over broadcast concessions.

A report by the World Association of Newspapers and News Publishers last year concluded that this kind of "soft censorship" was "an integral part of the country’s complicated media landscape." The researchers added that it was "a means to influence or even a tool to blackmail media owners and journalists."The effect, many analysts say, is to weaken critical news coverage. "Today the real estate scandals of the presidential family and their immediate circle are relegated to the inside pages, framed always by the official version," Jeszs Silva-Herzog Marquez, a political analyst and professor at the School of Government at Tecnolsgico de Monterrey, wrote in the daily newspaper Reforma on Monday.

Outside the capital, the situation is worse. Reporters face reprisals from organized crime and local officials, violence that has made Mexico one of the most dangerous places in the world to be a journalist, according to the New York-based Committee to Protect Journalists.

A report released last week by Article 19, a media watchdog group based in London, found that in Mexico, a reporter is harassed, threatened or attacked somewhere almost every day. The frequency has risen under Peqa Nieto’s government, the group said, and almost half of the attacks have been traced to government officials.

Aristegui, in a conversation with foreign reporters last week, said that if privileged journalists like those in her team could be attacked, "imagine the level of vulnerability for other journalists in Mexico."

Although there is no evidence that Aristegui was fired over the report on Rivera’s home, the perception that somebody in the federal government played a role in pressuring MVS has hardened. The company says that its disagreement with Aristegui is an internal issue.

The cause the company cited was her involvement, along with several of the reporters in the investigative team, in a new website called Mixicoleaks, designed to encourage whistleblowers to come forward and that guaranteed their anonymity.

Raphael said he thought that the government viewed Mixicoleaks with alarm because its investigations could uncover additional conflicts of interest. The site’s other collaborators are magazines and online newspapers with limited readership. But Aristegui’s large audience would have made investigations by Mixicoleaks national news.

"They are going after Carmen because she would have been its main voice," Raphael said.

MVS objected to the use of its name on Mixicoleaks without the company’s permission, fired the two lead investigative reporters and issued a list of editorial guidelines. One of the guidelines makes all news coverage subject to periodic evaluations by "specialized companies" and gives MVS the right to insert content in news programs.

After Aristegui refused to accept the guidelines, the company fired her and the entire investigative team on March 16. The guidelines would have created a "newscast that is malleable and subject to supervision, a newscast that wouldn’t have had the editorial freedom that it has had up to now," she said.

That freedom was not absolute. Aristegui chose to publish the report about the Mexico City mansion, known as the White House, on her own website, instead of broadcasting it on her morning program. She said last week that in the period leading up to the report, she had met with MVS’ chairman, Joaqumn Vargas, who told her that broadcasting the report on the radio would expose the company to too much risk. He asked for her "comprehension," she said.

In an emailed statement, Vargas refused to comment on whether such a conversation took place, citing the likelihood of a lawsuit from Aristegui. "It’s false that we censored Carmen Aristegui from broadcasting the report of the White House on MVS," he said, pointing to "hundreds of hours" of news coverage over the last four months.

MVS’ ombudsman, Gabriel Sosa Plata, has said that because of the way the dispute unfolded, including the presentation of the guidelines and a refusal by Vargas and his family to negotiate, "one could say that apparently there was indirect censorship."

Mariclaire Acosta, the director of the Mexico program at Freedom House, an organization based in the United States that focuses on media protection, was blunter. "Uncomfortable journalists will suffer reprisals," she said. Aristegui, she added, "touched political interests, and there were reactions."