Platinum producer Anglo American on Saturday declared force majeure on its deliveries of chrome from South Africa to customers.
The company said it has lost 67,000 ounces in production of platinum due to illegal strikes over the past four weeks, the equivalent of around 1.1 billion rands in revenues.
In a statement, Anglo American said:
''(The strike) will adversely affect the company's delivery obligations regarding the supply of chrome ore and, as a result, force majeure notices have been issued to its chrome customers".
However, AAP reports Anglo's ability to deliver other metals, including platinum and palladium, "remain(ed) unaffected at this stage".
Around 28,000 miners have been on strike for four weeks at Anglo's works at Rustenburg, which account for around a quarter of world platinum production. A week ago the company sacked 12,000 strikers.
Anglo American is the world's top platinum producer.
The mining industry accounts for around 20% of South Africa's GDP.
Standard Poor's cut South Africa's credit rating to -BBB with a negative outlook on Friday.