JAKARTA (APP) - Freeport McMoRan Copper & Gold Incs Indonesian workers union plans to extend a strike at the Grasberg mine by a month to Dec. 15, a union official said on Wednesday, taking it into the third month, the worst in the countrys mining industry. Workers have been on strike over pay since mid-September, slashing production at the worlds second-biggest copper mine and leading Freeport to declare a force majeure on concentrate shipments in late October. It was not clear if the unions latest move represented a hardening of its position, or simply was part of a process that requires it to give one weeks notice to the local government to be able to strike legally. The strike was due to end Nov. 15. This is a safety net. If we fail to find a solution, we can extend the strike and be protected by the law. We have already informed all parties this on Nov. 2, Virgo Solossa told Reuters. The strike will be automatically extended, that is the aim.