Istanbul is gearing up for Labor Day on Sunday, an occasion usually marked with violence. Areas to be closed to crowds include Taksim Square and surrounding streets, although protesters still plan to mark the day there.Labor Day, observed by labor unions across the country, has been eventful in past years, as protests frequently turned into riots led by left-wing groups and instigated by supporters of terrorist organizations. An umbrella body of labor unions insists on observing the day in Taksim Square despite having their application for a permit to protest rejected by local authorities. Several unions withdrew their request earlier this week and designated another square in Bakırköy on Istanbul's European side.Istanbul police announced on Friday that Tarlabaşı Boulevard, Mete, Gümüşsuyu and Sıraselviler streets leading to Taksim Square would be closed to traffic on Sunday, offering alternate routes for motorists through Kasımpaşa, Karaköy, and Beşiktaş.In Bakırköy, İsmail Erez Boulevard and surrounding streets will be closed to traffic. Ekrem Kurt Boulevard and a major road connecting the D-100 highway to Bakırköy's Halk Pazarı district where the rallies will be held are also closed to traffic throughout Sunday.Labor Day rallies in past years have been synonymous with confrontation between labor union members and police, as authorities have repeatedly banned rallies in Taksim, citing security reasons. Confrontation has led to riots almost every year in the past decade, with leftists taking the opportunity to attack police blocking the roads leading to Taksim. For many residents of the city, Labor Day means staying indoors instead of going about their daily business and avoiding areas around the city center to avoid intense tear gas fired by police, as well as a shower of stones and Molotov cocktails from demonstrators.Last year, members of labor unions and several radical groups clashed with police across Istanbul, and dozens of people were detained when they resisted the forced dispersal of rallies. Some threw stones and Molotov cocktails at riot police.Taksim Square was closed to Labor Day rallies from 1977 until 2010, following a massacre in the square in 1977 when unidentified gunmen opened fire on a crowd, leading to 37 deaths due to the gunfire and the ensuing stampede. Rallies in 2010 were peaceful, but after the ban was reinstated in 2012, protests again turned violent.Security measures will be tightened across the city. State-run Anadolu Agency reported that 6,000 police officers would be deployed in Bakırköy, while 15,000 police officers will be on duty across the city against possible riots. Deployed around rallies will be 120 armored vehicles with water cannons, while police helicopters circle crowds. Bomb disposal squads will also be deployed, while mass transit such as subway and metrobus services will be heavily policed.On Friday, unions held a commemoration ceremony remembering those who died in 1977 and laid flowers in Taksim Square amid tight security measures.Unions involved in Sunday's rallies and present for the commemoration ceremony on Friday include the Confederation of Progressive Trade Unions (DİSK), The Confederation of Public Sector Trade Unions (KESK), the Union of Chambers of Turkish Engineers and Architects (TMMOB) and the Turkish Medical Association (TBB).Speaking on the sidelines of the commemoration ceremony, DİSK Chairman Kani Beko stressed that labor unions were aware of the terror attacks over the past nine months that left hundreds dead in Istanbul and Ankara, referring to authorities' concern that such a massive rally in Istanbul can provide a target for terrorist organizations. In Şanlıurfa and Ankara, more than 130 people were killed in attacks in July and October blamed on DAESH suicide bombers. Both attacks targeted rallies drawing a similar left-wing demographic to those of DİSK members.The unions, which took part in the 2013 Gezi Park riots, nonetheless, see it as symbolic to protest in Taksim Square.