(REUTERS) -- Freeport McMoRan Copper & Gold Inc.'s Indonesia has told workers at its Grasberg mine not to work due to safety concerns linked to labor unrest, a union official said on Sunday.

Efforts by Freeport's Grasberg mine in the highlands of Papua island to get back to normal after a three-month strike last year have been hampered by protracted disputes between management and union workers, as well as by security concerns.

The mine is the second largest copper mine in the world and the largest gold mine and the strike rocked labor relations in Southeast Asia's biggest economy.

The decision by the company to ask workers not to work was an over-reaction and part of an effort to discredit union workers as trouble makers, said union spokesman Juli Parorrongan, adding that there was some friction between union and non-union workers.

PT Freeport Indonesia has initiated 'shut-down' procedures, according to a confidential memo dated Feb 23 that was obtained by Reuters. We will not conduct operations amid situations where we cannot provide a reasonable assurance of safety and security, said the memo, which the company declined to confirm.

Intimidation and violence by some workers against others who did not take part in last year's strike have disrupted the mine, the company said on Thursday.

The Grasberg strike ended Dec. 14 with a deal for a pay increase, allowing workers to gradually return to work, but the force majeure has yet to be officially lifted.