ISTANBUL (Reuters) - Construction workers at Istanbul’s new airport resumed work on Monday, with heavy police and gendarmerie presence at the site, two labor unions told Reuters, after protests last week over work conditions.

The airport is a centerpiece of a 15-year construction boom under President Tayyip Erdogan. 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.

Workers have long complained about food, housing and work safety conditions at the construction site, which unions have likened to a concentration camp.

In February, Turkey’s labor ministry said 27 workers had died at the airport since the start of work in 2015, mainly from accidents or health problems. Protests started on Friday after a shuttle bus accident injured 17 workers.

“The reason the majority of our friends have resumed work is not because their requests were met by the company,” said Ali Oztutan, president of IYI-SEN Union.

Oztutan said there was a heavy security presence at the airport, which is due to open next month, and that workers were pressured to resume work with threats to not pay them, lay them off or detain them.

Ozgur Karabulut, general manager of Dev Yapi-Is Union, said it was not clear whether the protests would continue.

“The housing area is full of police and gendarmerie, they won’t even let the workers breathe,” he said, adding that 162 workers were still detained.

Istanbul Governor Vasip Sahin said on Sunday that 401 workers had been detained for taking part in the protests.

Airport operator IGA said on Sunday that work at the airport was on schedule and the planned Oct. 29 opening would not be delayed. Steps had been taken to improve working conditions and living quarters, which workers say were infested with bedbugs, it said.

Veli Agbaba, parliamentarian from the main opposition Republican People’s Party (CHP), said authorities did not allow him and others within 10 km (6 miles) of the construction site on Monday.

“There is nothing that cannot be solved in the requests of the third airport workers,” he said, calling on the labor ministry to investigate the claims of poor work safety conditions.