Turkish police detained 77 people who defied a ban to mark May Day at Istanbul’s Taksim Square, the traditional protest site that still remains contentious four decades after dozens of leftists were killed there during May Day celebrations.

Authorities deployed more than 26,000 police officers around the city, cordoned off Taksim Square with metal barricades and suspended public transit and traffic on roads leading to the key transport hub to prevent marchers from reaching the space. Helicopters patrolled the skies above the square.

The extraordinary measures underscore President Recep Tayyip Erdogan’s determination to keep a lid on potential unrest ahead of elections to be held June 24 under the continuing state of emergency. The historic vote, which Erdogan pulled forward by 17 months, will usher in constitutional changes that will vastly expand the powers of the president and formally sideline the parliament.

Hundreds of tourists struggled to reach hotels or leave for the airport from Taksim, a major tourism center, reported CNN Turk, showing footage of them dragging suitcases past riot police.