Thousands of people are expected to defy a government ban to gather on Istanbul's highly symbolic Taksim Square Thursday, a year after May Day clashes helped launch a nationwide protest movement.
Prime Minister Recep Tayyip Erdogan has warned protesters to "give up hopes" of meeting on Taksim, a traditional and symbolic rallying point, but activists have vowed to ignore the ban and a massive police presence, raising tensions to a fever-pitch ahead of the workers' holiday.
Violent protests between police and protesters on May Day last year were followed weeks later by protests that snowballed into one of the biggest challenges to Erdogan's rule.
Last week Erdogan said he would "not tolerate" any demonstration on the square, saying: "Give up on your hopes of Taksim. Do not engage in a fight with the state. Do not disturb the peace of our people".
Istanbul Governor Huseyin Avni Mutlu added Wednesday that intelligence reports indicated "illegal terrorist groups" were planning unrest at Taksim, making the ban necessary.
Turkish media meanwhile reported that 40,000 police officers as well as dozens of water cannon trucks and armoured vehicles would be deployed to Istanbul on 1 May, with roughly half of the city's police force drafted into the centre to block access to the square.
But leftist unions and the opposition have vowed to ignore the ban.
On Wednesday, the so-called 1 May committee -- made up of unions and civil society groups -- said that they would "defy an irrational, unlawful ban".
"All roads will lead to Taksim on 1 May," Kani Beko, the head of the DISK union, said in a statement on behalf of the committee.
As an alternative to Taksim, the government has suggested a rally area in Yenikapi, a reclaimed land overlooking the Marmara Sea where Erdogan's Islamic-rooted Justice and Development Party (AKP) held a massive rally in the run up to the March 30 local elections.
The government has also offered free transport to Yenikapi while limiting Istanbul public transport to make it more difficult to access Taksim Square.