Turkish police have detained hundreds of workers protesting over labor conditions at Istanbul’s new airport, a giant project championed by President Tayyip Erdogan and due to open next month, a union leader said on Saturday, Reuters reported.

The protest broke out after a shuttle bus accident on Friday in which 17 workers were injured, said Ozgur Karabulut, general manager of the Dev Yapi-Is union.

Thousands of workers joined the demonstration, which was broken up by police and gendarmes deploying in riot control vehicles and firing tear gas, he said.

“They broke into the workers’ camp with 30 gendarmerie, broke down the doors and detained around 500 workers,” Karabulut told Reuters by phone. He said he was speaking from a local gendarmerie where he was seeking the workers’s release.