First Quantum Ltd.’s copper mine in Panama is winding down operations as a blockade of small boats at a port restricts key supplies such as coal for energy, a union leader said.

Workers continued to leave the site early Thursday, Michael Camacho from the Utramipa union said in text messages. He urged the government and police to intervene in the port blockade in order to get back to work.

“We are worried as a union because the authorities do not say anything,” Camacho said.

First Quantum, which didn’t immediately provide a comment, had warned it would be forced to shut the mine if the blockade continued to prevent the delivery of supplies. Operations started slowing last week.

Read More: First Quantum Prepares to Halt Panama Copper Mine This Week

The Canadian firm has found itself at the center of a political storm in Panama, with the future of its massive Cobre Panama mine called into question after widespread protests erupted last month over a deal to renew an operating contract. President Laurentino Cortizo announced a referendum on the mine, although the vote has been shelved as the government waits for a Supreme Court ruling over whether to revoke the mine’s contract.