Early results indicated a 51โ49% lead for the "Yes" vote. In an unprecedented move, the Supreme Electoral Council (YSK) allowed non-stamped ballots to be accepted as valid. Some critics of the reform decried this move to be illegal, claiming that as many as 1.5 million ballots were unstamped, and did not recognize the results.
Large-scale protests erupted following the results in order to protest the YSK's decision. In subsequent reports, the Organization for Security and Co-operation in Europe (OSCE) and Parliamentary Assembly of the Council of Europe (PACE) both criticized unfairness during the campaign and declared the YSK's decision to be illegal.
An executive presidency was a long-standing proposal of the governing AKP and its founder, the current President of Turkey, Recep Tayyip Erdoฤan. In October 2016, the Nationalist Movement Party (MHP) announced its co-operation for producing draft proposals with the government, with the combined support of both AKP and MHP MPs being sufficient to put forward the proposals to a referendum following a parliamentary vote in January.
Those in favour of a "Yes" vote argued that the changes were necessary for a strong and stable Turkey, arguing that an executive presidency would bring about an end to unstable coalition governments that had dominated Turkish politics since the 1960s up until 2002. The "No" campaign argued that the proposals would concentrate too much power in the hands of the President, effectively dismantling the separation of powers and taking legislative authority away from Parliament.
Three days before the referendum, one of Erdoฤan's aides called for a federal system should the "Yes" vote prevail, causing a backlash from the pro-Yes MHP. Both sides of the campaign were accused of using divisive and extreme rhetoric, with Erdoฤan accusing "No" voters of being terrorists siding with the plotters of the failed 2016 coup.
The campaign was marred by allegations of state suppression against "No" campaigners, while the "Yes" campaign was able to make use of state facilities and funding to organize rallies and campaign events. Leading members of the "No" campaign, which included many high-profile former members of the MHP such as Meral Akลener, รmit รzdaฤ, Sinan Oฤan, and Yusuf Halaรงoฤlu, were all subject to violence and campaign restrictions.
The "Yes" campaign was faced with campaigning restrictions by several European countries, with the German, Dutch, Danish and Swiss governments all cancelling or requesting the suspension of "Yes" campaign events directed at Turkish voters living abroad. The restrictions caused a sharp deterioration in diplomatic relations and caused a diplomatic crisis between Turkey and the Netherlands.
Concerns were also raised about voting irregularities, with "Yes" voters in Germany being caught attempting to vote more than once and also being found to have been in possession of ballot papers before the overseas voting process had started. European election monitors said the vote did not meet international standards.
Background
Introducing a presidential system was proposed by then-Minister of Justice Cemil รiรงek and backed by then-Prime Minister Erdoฤan in 2005. Since then, the current presidential system has been openly supported by Justice and Development Party leaders several times, along with a "new constitution". Justice and Development Party vice-president Hayati Yazฤฑcฤฑ proposed April 2017 as a date for the referendum.
The parliamentary system formally began transforming into a centralised presidential system after President Recep Tayyip Erdoฤan won the July 2018 elections. Since its inception, there have been competing arguments for and against this transformation.