The Chennai Police on Thursday detained at least 10 students who tried to stage a protest in the city against the reopening of the Sterlite copper smelter plant in Thoothukudi, reported The New Indian Express.

The National Green Tribunal last week set aside the Tamil Nadu government’s order to shut down the copper plant run by Vedanta, calling it unjustifiable. Protests have also erupted in Thoothukudi against the tribunal’s decision to let Vedanta resume operations, with several residents hoisting black flags which were reportedly removed by police, according to India Today.

According to police, 10 members of a student organisation based in Thoothukudi gathered near the Press Club in Chennai around 11 am on Thursday, carrying placards with anti-Sterlite messages. An unidentified police official said three of the 10 members were school students, while the remaining were college students.

“We came to know that students from Thoothukudi will be arriving at Chepauk around 10.30 am on Thursday to protest against Sterlite’s reopening,” a police official said. “We detained them as a preventive measure and will release them by evening.”

Thoothukudi coordinator of the All College Students Federation, K Santosh, said the state government was clamping down on peaceful protests by villagers around the plant, while youngsters are being warned of arrest, reported The Hindu.

For two decades, activists and residents have protested against the plant, saying that it has contaminated the air and water in the region and caused health problems. At least 13 people protesting against the expansion of the copper smelter were killed on May 22 and May 23. This had prompted the state government to permanently shut down the plant days later.