Workers from South Africa's mainly white Solidarity union staged a go-slow protest at the petrochemicals firm Sasol on Monday over a share scheme offered exclusively to black staff, and said they would begin a full strike on Thursday.
South African companies are required to meet quotas on black ownership, employment and procurement as part of a drive to reverse decades of exclusion under apartheid.
Sasol, the world leader in technology that converts coal and gas to fuel, has sold 25 percent of its local operations to qualifying black employees, a foundation and the black public in a 21 billion rand ($1.42 billion) deal financed by the company.
It has said the scheme is not a benefit but a mechanism designed to meet the rules on black economic empowerment.
But Solidarity said the scheme was discriminatory and that it would file a complaint to U.S. regulators. Sasol also operates in the United States.
Solidarity said its 6,300 members would hold a go-slow at Sasol's facilities in South Africa, and then strike on Thursday.
Dirk Hermann, Solidarity's chief executive, said the union would file its complaint in the U.S. by early next week.
The union said the scheme excluded both white staff and foreign nationals.
"We are not against the scheme, we just want it to be inclusive of all workers. If the company makes it inclusive, the majority will still be black, so we see no need to exclude white workers as this is discrimination," Herman said.
Sasol, which employs around 26,000 people in South Africa, said it was aware of Solidarity's intent to strike.
A Sasol spokesman said he would give an update on the go-slow later in the day.
Sasol's shares were 0.6 percent lower at 572.29 rand.
"It depends on the duration of the strike, at this point there is little impact," said Wilmar Buys, a director at FFO Securities. "The stock is being propped up by the weaker rand and higher oil price at this point in time."
A weaker rand strengthens Sasol's earnings because most of its products are sold in dollars.
South Africa's rand traded nearly a percent lower as demand for emerging market currencies weakened. Oil prices rose, supported by concerns that falling Iranian output will tighten markets once U.S. sanctions start biting.