Turkey is holding a national referendum Sunday to approve or reject a package of constitutional reforms that would replace the country’s parliamentary system with a presidential one. The referendum is seen by many as the ultimate test of President Recep Tayyip Erdogan’s popularity.

The Vote

More than 55 million people are eligible to cast votes in some 167,000 ballot boxes at polling stations across the country. Close to 3 million expatriate Turkish citizens in 57 countries were also eligible to vote between March 27 and April 9 at Turkish diplomatic missions.

Polls open at 7-00 a.m. (0400 GMT) and close at 4-00 p.m. (1300 GMT) Sunday in 32 eastern provinces, and open and close an hour later in the rest of the country. Turkey has no official exit polls and media are barred from publishing or broadcasting election results until the High Election Board lifts the ban at 1800 GMT or earlier.

The Main Issues

The “yes” camp argues that the proposed changes for a strong presidency will create a robust and stable Turkey, while the “no” side says they would give the office of the president too many powers with very few safeguards.

If approved in the referendum, the changes would transfer executive powers currently held by the prime minister to the president. The prime minister’s office would be abolished. The president would have the powers to dismiss ministers, issue decrees, declare a state of emergency, and make appointments to key positions.

The president would be able to remain a member of a political party or even lead it ending the tradition of presidential impartiality. Under the current Constitution, presidents are required to severe ties with their parties.

Other Changes

The president can be elected for two consecutive five-year terms.

Referring the president to the country’s top court for possible impeachment would require a two-thirds parliamentary majority. The parliament would not be able to bring down a government or a minister in a vote of no confidence. The ruling party argues that the changes will remedy the current system under which the president can only be tried for treason. Presidential and legislative elections would be held at the same time. If the president dissolves parliament, then both parliamentary and presidential elections will be renewed.

The reforms would increase the number of seats in parliament from the current 550 to 600. The age of candidacy for a parliamentary seat would be lowered from 25 to 18.

The Campaign

The “yes” campaign backed by Mr. Erdogan, Prime Minister Binali Yildirim and the ruling Justice and Development Party has dominated Turkey, while the opposition “no” camp have faced threats, violence, arbitrary detentions, a lack of TV airtime, and disregard by pro-government media.

The main opposition Republican People’s Party, or CHP, says it has counted more than 100 incidents of obstructions to the “no” campaign, ranging from physical assault to death threats. Mr. Erdogan and government officials are accused of using state resources and official functions such as openings of infrastructure projects to campaign in favor of the changes.

Campaigning took place under a state of emergency imposed following last summer’s failed military coup attempt. More than 150 media outlets have been closed and some 150 journalists jailed. About a dozen legislators from Turkey’s opposition pro—Kurdish party are also in prison. An emergency rule decree has removed the Supreme Electoral Board’s powers to fine media who do not provide impartial coverage.

Security

Turkey has suffered from a series of violent attacks and bombings since 2015, linked to the resumption of conflict with Kurdish rebels in the southeast and increased activity of foreign and domestic Islamic State group cells in Turkey.

More than 250,000 police officers and nearly 130,000 paramilitary police will be on duty on Sunday, in addition to some 6,000 military personnel on stand-by, Interior Minister Suleyman Soylu said.