Unionised coal miners in Australia have voted to accept an employment contract offer by BHP Billiton following two years of industrial action, the workers' union said on Monday.

Workers at five mines, operated by BHP and co-owned by Mitsubishi Corp of Japan <8058.T>, supplying a fifth of the world's traded metallurgical coal, restarted talks in July in hopes of resolving the dispute.

BHP, the world's biggest diversified mining company, in April invoked a declaration of force majeure as it struggled to meet overseas supply contracts, in part due to a barrage of rolling work stoppages staged by some 3,500 union workers at the mines, representing a third of the total workforce.

Force majeure is a legal move releasing companies from supply obligations due to circumstances beyond their control.

In a ballot conducted last week and tallied on Monday, the latest offer, which boosts company retirement fund contributions, was approved by 60 percent of voters, the Construction, Forestry, Mining and Energy Union said.

"It could have been reached a year ago had BHP not taken an ideological approach that prioritized picking a fight with its work force over coming to a reasonable deal," the union said.

BHP said it in a statement it was pleased to have finally reached an agreement.

(Reporting by James Regan; Editing by Ed Davies and Richard Pullin)