The firing of a prominent news anchor for his objection to constitutional changes that would expand presidential powers is the latest development to highlight Turkey's tightening choke hold on critical voices ahead of a referendum that the opposition considers unfair.

On April 16, Turkey will vote in one of the most critical polls in its modern history, deciding whether to change the country to an executive system, which would grant President Recep Tayyip Erdogan the sweeping powers that he has long sought.

If approved in the referendum, the constitutional changes greenlighted by parliament last month would, among other things, give Erdogan the power to dismiss ministers and dissolve parliament, issue decrees, declare emergency rule, and appoint figures to key positions, including within the judiciary.

Kanal D sacked anchor Irfan Degirmenci on Saturday, a day after he came out against the proposed constitutional amendments in a series of 20 tweets to his 1.7 million followers. The national television channel claimed that Degirmenci was let go because he violated policy by "clearly taking a side on an issue the public is debating."

"No to the one who views scientists, artists, writers, cartoonists, students, workers, farmers, miners, journalists and all who do not obey as the enemy," Degirmenci wrote on Friday, releasing a series of critical tweets to back up his "No" vote.

Social media users and the opposition were quick to call Kanal D hypocritical, pointing out that the journalist Fatih Cekirge had openly supported the presidential system but was not fired. Veli Agbaba, the deputy head of the main opposition Republican People's Party (CHP), called the sacking "the result of pressures against the 'No' vote and a clear sign the referendum will not be carried out under equal conditions."

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A one-sided argument

Erdogan's supporters argue that Turkey needs a strong leader to make decisions after last July's failed coup attempt and a string of terror attacks. Opponents say the changes would further strengthen an authoritarian leader and turn Turkey into a full-blown dictatorship with few checks or balances.

The opposition media has been under assault in Erdogan's Turkey: Dozens of journalist are in jail, at least 150 outlets have been shut over the past year, and self-censorship is the norm.

The media landscape is dominated by pro-government outlets, most owned by large holding companies that are either close to the government or afraid of taking a stand lest they become targets themselves. Holding companies with media assets often rely on the government for lucrative contracts in other areas where they conduct business.

Kanal D, for example, is owned by Dogan Holding, which owns several major newspapers and television channels, including CNN Turk. Dogan Holding's media empire is relatively neutral compared to pro-government mouthpieces.

Erdogan has even been known to personally call up the heads of news organizations to complain about coverage.

Pro-government media are ramping up support for the referendum and crowding out or ignoring the voices of opponents. The echo chamber in the media created around Erdogan and his supporters tips the balance of information creation toward the side of the government.

On Saturday, Erdogan, echoing other recent statements from Prime Minister Binali Yildirim, likened a vote against the presidential system to supporting the Kurdistan Workers' Party or July's failed coup. That is a serious statement, considering tens of thousands of people alleged to have ties to Kurdish insurgents or coup plotters have been thrown in prison or lost their jobs.

A dearth of unbiased information about what the constitutional amendments mean and the pro-government slant in coverage has raisedconcerns about the vote's legitimacy.Adding to worries about the openness of debate, the referendum campaign is set to take place under a state of emergency.

"The referendum process will not take place under fair conditions," Kemal Kilicdaroglu, the head of the CHP, told journalists on Saturday. "We know that the (pro-government media) will continue to act as though the opposition does not exist."

The CHP and pro-Kurdish Peoples' Democratic Party - which has been weakened by the arrests of hundreds of its members, including a dozen parliamentarians - oppose the referendum. Erdogan's Justice and Development Party and the right-wing Nationalist Movement Party support the expanded presidential powers.