Sasol recently introduced a new 10-year staff share scheme, Khanyisa phase 2, which excludes white workers and foreign nationals, something the union's Dirk Hermann says is “causing racial tensions on the work floor”.

However, Sasol has defended its decision, saying the scheme is designed to boost black ownership within the company, as part of the legislated Black Economic Empowerment (BEE) programme which seeks to redress historic inequalities in South Africa.

Mr Hermann, speaking to the BBC, said the union had chosen to go on strike after months of getting no joy from the company. "The company is in the middle of a scheduled three-week maintenance programme. The union has chosen to go on strike at the same time to ensure that the effects of the strike are felt."

Delays in the maintenance programme will cost the company huge sums of money and many of the union’s members are technical staff and artisans and are needed to carry out the maintenance programme at various sections of the plant.

The Khanyisa share scheme is the second employee related incentive scheme in recent years. In a previous scheme, known as Inzalo, all workers could take up share ownership. Mr Hermann said the change is purely aimed at earning Saso, BEE status with the government and was not meant to benefit workers.

The strike action will include go-slows and lunchtime pickets, the union said.