(Adds union comment, background)
LIMA, May 5 (Reuters) - Workers at Peru's biggest copper mine, Freeport-McMoRan Inc's FCX.N Cerro Verde, were evaluating whether to strike, a union spokesman said on Friday, after the union said the company had threatened punishment for a previous work stoppage.
Unionized workers at Cerro Verde went on strike in March to demand improved benefits, hitting output at the mine. It ended after three weeks when the union accepted the company's offer. Freeport, the world's top copper miner by output, had said it would temporarily suspend workers who took part in the strike without pay, and would sack them if there were another "measure of force," union secretary general Zenon Mujica told Reuters.
Mujica said that if the company insisted on its plan, then the union would consider a new, indefinite strike. The union is also preparing legal protections against the company's measures, he said.
Freeport did not immediately respond to requests for comment. It has previously said that it strictly complies with its obligations by law and under union agreements.
"The only way we can suspend our measure of force is if the company retracts its position of applying sanctions," said Mujica. "This is an abuse because it is ignoring the right to strike that is in the Peruvian Constitution."
The union would meet Friday afternoon to discuss next steps, he said, and look to meet with government officials next week to try to resolve the dispute.
Cerro Verde became Peru's biggest copper mine following an expansion in 2015, as it churned out nearly 500,000 tonnes of copper last year.
Freeport owns just over 53 percent of Cerro Verde. Sumitomo Metal Mining Co Ltd 5713.T and Buenaventura BVN.N BUEv.LM both hold smaller stakes.