(Reuters) – Workers at South Africa’s state-owned logistics firm Transnet will go on strike starting this Thursday over a wage dispute, two labour unions said, in a move that could halt the export of key minerals and other cargo.

Transnet has been operating below capacity due to a shortage of locomotives, poor maintenance and vandalism and theft of its infrastructure, costing miners billions of rand in potential revenue. A strike would paralyse freight rail services and impact South Africa’s ports, also managed by Transnet.

The United National Transport Union (UNTU), which is the biggest labour union at Transnet, said it had served notice to begin industrial action on Thursday. The other union at Transnet, South African Transport and Allied workers Union (SATAWU), said it would join in the strike from Monday.

Both unions said Transnet’s offer of a 1.5% pay increase from Oct. 1 fell below their demands.

“Transnet…must provide a salary increase offer that is aligned with the increased cost of living, cost of housing, medical costs, housing and, of course, the consumer price index (CPI) that is currently running at 7.6%,” UNTU said in a statement.

Transnet has said any increase beyond its current wage offer would not be sustainable.

“Transnet has consistently made the point that its wage bill currently makes up over 66% of monthly operating costs. This is not sustainable, particularly given the current operational and

financial performance,” it said in a statement on Tuesday.

Transnet has applied to the Commission for Conciliation, Mediation and Arbitration (CCMA), a state agency that mediates labour disputes, for further talks with the unions.

Both UNTU and SATAWU said the mediation, which is due to start on Oct. 12, would not affect their plans to go on strike.

($1 = 17.7281 rand)

(Reporting by Nelson Banya, Editing by Louise Heavens)