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. No question is written on the ballot paper and it is assumed that the people know what they are voting for. The wide ranging reforms propose giving the president the powers to appoint ministers, set the budget, issue laws by decrees on a wide range of issues, dissolve parliament and declare a state of emergency.
Nonetheless, Turkey needs a "no" on Sunday. But the bigger issue is that it would result in sweeping new powers for President Recep Tayyip Erdogan.
If passed, the new presidential system will implement the most radical political shake-up since the fall of the Ottoman Empire, dispensing with the office of the prime minister and centralising the entire executive bureaucracy under the presidency.
Former prime minister Ahmet Davutoglu spoke before Erdogan at a "Yes" rally in the Anatolian city of Konya on Friday but, to the amusement of opposition commentators, failed once to endorse the presidential system.
Approval could see him stay in office until 2029. Until recently, the president was an appointed position serving as head of state, not head of government - similar to the queen of England.
Under the current constitution, Erdogan can run for a second five-year term in 2019 and serve until 2024. The change, he says, will bring much-needed stability to Turkey.
The reforms would extend the president's executive powers and the president would also be allowed to retain ties to a political party.
Erdogan has an incentive to call a snap election swiftly if he secures a "yes" vote in the plebiscite, since the new powers he has long sought would take effect only after fresh elections for president and parliament. In theory, each institution could keep the other in check by keeping a finger on the eject button: the president and the parliament would be able to cut short each other's mandates, as well as their own, by calling early elections.
Presidential and legislative elections would be held at the same time.
The country's current constitution was formed in 1983 following a military coup in 1980. The age of candidacy for a parliamentary seat would be lowered from 25 to 18.
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.
The report also said that the freedom of expression had been further restricted by the closure of numerous media outlets and the arrest of a large number of journalists in the wake of the failed coup.
According to Karan, although "yes" campaigners now slightly lead in polls, it is hard to make any predictions, and political tension in the country is extremely high.Since the failed coup in July 2016, more than 130,000 teachers, civil servants, academics and state officials have been fired, and almost 50,000 arrested, according to Turkey Purge.
"Erdogan has also abandoned the ambitious foreign policy that boosted Turkey's economy and helped increase the country's role in global affairs, replacing it with a crude nationalism", wrote Elmira Bayrasli, a professor at Bard College.