(REUTERS) -- Pressure built on an Indonesian firm on Wednesday to resolve a local dispute with workers at a Freeport McMoran Copper & Gold Inc. mine that has prompted the union to halt a return to work after a three-month strike.

The union said there would be no mobilisation to return to work on Wednesday and not until contractor PT Kuala Pelabuhan Indonesia (KPI) guaranteed that workers who took part in the strike would not be penalised.

The delay will push back the resumption of full operations at the world's second-biggest copper mine, which is on Papua island, eastern Indonesia. Arizona-based Freeport earlier said it expected full operations at the Grasberg mine to resume in early 2012.

There's no mobilisation today. If there's no mobilisation, automatically there's no work. Principally we're just waiting now for KPI, union spokesman Virgo Solossa said by telephone.

The strike was settled on Dec 14 when the union and Freeport agreed to a pay increase of roughly 40 percent for around 8,000 union members and to a framework for a better deal for roughly 15,000 other non-union workers and contractors.

The resolution, while not all the union wanted, is a watershed in relations between employers and workers demanding a greater share of the spoils in southeast Asia's largest economy at a time of rapid economic growth.

Workers have not returned immediately to the mine because of delays in organizing transport for thousands of miners in the highlands of central Papua where security is tense because of a low-level separatist insurgency and concerns that returning strikers would be penalised.

Police on Papua also urged KPI to resolve the dispute.

Contractors must follow the spirit of the agreement between Freeport and its union so that striking workers can return to work with a clean slate, no bad records on them, Mimika police chief, Denny Siregar, told Reuters by telephone.

The police were acting as an unofficial mediator in the dispute that only emerged at the tail end of the strike, Siregar said.

KPI sacked 18 workers who failed to show up during the strike, which began on Sept 15. It will allow 473 other workers to return under certain conditions, KPI senior manager for corporate and administrative support, Juarsa Oemardikarta, said in an email.

KPI is also evaluating the status of 101 workers who have been suspended, Oemardikarta said. They were being asked to sign a document agreeing not to join a union, according to Maskat Kaliky, secretary general of the KPI union who said he had not seen the document.

Contractor KPI runs the Freeport port through which concentrate is shipped. It also operates road and transport facilities as well as mobile equipment and employs 2,100 workers.