ISTANBUL (Reuters) - Most construction workers who were detained after protests over labor conditions at Istanbul’s new airport were released on Sunday, the city’s governor said, but a union leader said hundreds were still held and more protests were likely.

Turkish Gendarmes surround workers during a protest against the labor conditions at the construction site of the city's new airport in Istanbul, Turkey September 14, 2018. Picture taken September 14, 2018. Akin Celiktas/Demiroren News Agency via REUTERS

The airport, a centerpiece of a 15-year construction boom under President Tayyip Erdogan, is due to open late next month. It has an initial planned capacity of 90 million passengers a year, making it one of the world’s biggest airports and a pillar of Turkey’s lucrative tourism industry.

Unions say workers at the site have long complained about conditions, including pay, food and living quarters, as well as safety standards. In February, Turkey’s labor ministry said 27 workers had died at the airport since the start of work there in 2015, mainly from work accidents or health problems.

Protests broke out on Friday after a shuttle bus accident injured 17 workers.

Thousands of workers joined the demonstration, which was broken up by police who deployed in riot control vehicles, one union leader said.

Video footage, which the union said was from the construction site, showed hundreds of men chanting: “We are workers, we are right. We will have our way one way or another.”

Large labor protests have been rare in Turkey since a state of emergency was imposed following a failed July 2016 coup. It was lifted two months ago after Erdogan’s re-election but his opponents say Turkey’s new executive presidency retains many of the emergency powers.

Istanbul Governor Vasip Sahin said 401 people had been detained, either for refusing to work or “trying to provoke others”, according to Hurriyet newspaper. It quoted him as saying 275 were released on Sunday morning and the airport operator had started “addressing the problems.”

Ozgur Karabulut, general manager of Dev Yapi-Is union, said on Sunday that 160 people had been released and the union estimated 360 remained in detention.

“Some of our friends who were released last night were taken back to the camps but they are not working,” he told Reuters, questioning whether the airport would be ready to open on schedule. “We expect these protests to go on for a long time.”

A statement issued on Sunday by unions complained of late salary payments, poor food and “awful” conditions at the workers’ living quarters. The “airport construction site is no different to concentration camp for workers,” it said.

An official at airport operator IGA played down the protests, saying work continued and the airport would open as planned on Oct. 29.

“Our workers are working to schedule, there is no disruption at all,” IGA’s corporate communications director Gokhan Sengul said. “There was a little bit of protests on Friday triggered by provocateurs who came in on Friday like union representatives.”

Sengul said the company had already started improvements, including disinfecting rooms and laying on extra buses to prevent delays to and from work.

“All this talk about protests is just manipulation... We are due to open on October 29 with no disruption,” he said.