Police in Peru fired tear gas and rubber bullets on Tuesday at opponents of Southern Copper’s $1.4 billion proposed Tia Maria mine in protests that threatened to further delay the project.

The company said early last month that it expected to receive a building permit by the end of March following the government’s key approval of its environmental plan last year.

Peru had rejected Southern Copper’s first environmental plan amid a wave of protests that turned deadly in 2011.

Protesters on Tuesday called for the government to nix the project because they say it will pollute agricultural valleys, said rice farmer and activist Juan Carrasco, 58.

“We’re going to keep protesting tomorrow and everyday until Tia Maria leaves,” Carrasco said.

Three protesters were wounded and two arrested in the clashes in Peru’s southern region of Arequipa, said local police chief Enrique Blanco.

TV images showed police firing tear gas at a crowd on a highway and protesters running into nearby fields.

Blanco said between 600 and 700 protesters, mostly women, took part in the march on Tuesday – the second day of protests. Carrasco said there were at least 3,000.

The Interior Ministry said it had sent 2,000 police to the region ahead of the protest to control potential unrest.

The energy and mines minister traveled to Arequipa last week in a bid to resolve differences with opponents.

The Energy and Mines Ministry and Southern Copper said they could not immediately respond to requests for comment.

Southern Copper, controlled by Grupo Mexico, had said it planned to start work on Tia Maria upon receiving the construction permit, usually a formality in Peru after the environmental plan is approved.

The project is expected to produce about 120,000 tonnes of copper per year.

Several mining projects in Peru, the world’s third top copper producer, have been suspended in the past decade because of local opposition, including Newmont Mining Corp’s $5 billion gold and copper Conga project, Bear Creek Mining Corp’s proposed Santa Ana silver mine, and Zijin Mining Group Co Ltd’s Rio Blanco project.