Trade union Solidarity general secretary Gideon du Plessis said the Chamber of Mines raised its offer 0.5% to a 7% wage increase for coal industry employees.

The offer included a 7% increase in employees’ housing allowance, du Plessis said in a statement sent to Bloomberg.

The talks began last month with a proposed 4% increase in basic pay and incremental increases have been repeatedly rejected by the unions.

Declaring a dispute moves the matter into arbitration.

If the next stage of talks at the Commission for Conciliation, Mediation and Arbitration fail to break the standoff, the companies may face more strike action.

The Chamber of Mines represents coal companies in the negotiations including Anglo American, Exxaro Resources, BHP Billiton Energy Coal and Coal of Africa.

Often-violent labor unrest shut parts of South Africa's mining industry for months last year and the industry remains anxious about a renewal of the disturbances that left more than 50 people dead and pushed prices higher.

Du Plessis said South Africa’s largest union, the National Union of Mineworkers, had also joined the dispute.