There is little disagreement on how pivotal that change could be. AP observed that the vote “could change the course of [Turkey’s] history,” while AFP reported that referendum is being regarded “as a crossroads in the modern history of the country that will affect not just the shape of its political system but also its relations with the West.”

The vote is taking place against the backdrop of a widespread crackdown on dissent, with tens of thousands of people arrested under the ongoing State of Emergency declared by Erdoğan after last summer’s failed coup attempt.

Recent polling has shown that the public is split. According to AFP, “A poll by the Konda group showed ‘Yes’ ahead at 51.5 percent but the Sonar group has projected a ‘No’ vote of 51.2 percent, and with other polling companies producing different figures the outcome remains uncertain.”

But observers note that surveys could be misleading, given the climate of fear and repression. “[P]redictions cannot be trusted,” Turkish author and activist Elif Shafak wrote Friday. “The truth is, many people in Turkey have two opinions: a public opinion and a private opinion. Out of fear, many citizens refuse to share their private opinions with pollsters.”

On Thursday, four United Nations special rapporteurs criticized the Turkish government, issuing a statement warning that the security crackdown “had undermined the chance for informed debate on the referendum. They said a state of emergency imposed after the abortive putsch had been used to justify repressive measures that might well intensify if Erdoğan’s powers are enhanced,” Reuters reported.

Hallinan also recently outlined how Erdoğan has “stacked the deck” for the vote:

Using last summer’s failed coup as a shield, he’s declared a state of emergency, fired 130,000 government employees, jailed 45,000 people—including opposition members of parliament—and closed down 176 media outlets. The opposition Republican People’s Party says it’s been harassed by death threats from referendum supporters and arrests by the police.

Meanwhile he’s deliberately picked fights with Germany, Austria, and the Netherlands to help whip up a storm of nationalism, and he charges that his opponents are “acting in concert with terrorists.” Selahattin Demirtas, a member of parliament and co-chair of the Kurdish-dominated People’s Democratic Party, the third largest political formation in Turkey, is under arrest and faces 143 years in prison. Over 70 Kurdish mayors are behind bars.

Erdoğan’s AKP government, Shafak further noted, “is supported by the far-right and Euro-skeptic MHP (the Nationalist Movement party). Together they form the largest bloc in the parliament.”

“The opposition is fragmented, disorganized,” she added, noting that it includes the secularist CHP (the Republican People’s party), the Kurdish community, and Turkish conservative leader Meral Akşener.

“But the staunchest opponents of the AKP-MHP bloc are ordinary Turkish citizens,” Shafak said: “Students, professionals, artists, minorities, and especially feminists. The women’s movement in Turkey is going through a transformation and revival. This is not a coincidence. When societies slide into authoritarianism, ultranationalism and fanaticism, women have much more to lose than men. Women have been holding anti-AKP rallies. They organize campaigns on social media, writing hayir (no) with their bodies, urging everyone to hang purple cloth from their windows and balconies as a sign of support for gender equality.”

If the referendum passes, the changes will take effect with the next general elections, which are slated for 2019.