Workers from South Africa's mainly white Solidarity union started a go-slow protest at petrochemicals firm Sasol over a share scheme offered exclusively to black staff, and will launch a full strike on Thursday.
The Solidarity union also said it will file a complaint to US regulators over Sasol's "discriminative" black share scheme.
The company is a leader in technology that converts coal and gas to fuel and also operates in the US.
"We have a staggered industrial action. Today, we have a go-slow. Our 6 300 members will carry out their duties, but in a slow manner. We plan to ramp up to a full-blown strike on Thursday," Dirk Hermann, Solidarity's chief executive said.