The National Union of Metalworkers of South Africa (NUMSA) began a strike at Africa's biggest steel company on Wednesday, after wage negotiations broke down last week.
South Africa's labour court on Wednesday ordered that workers at the company's steel plants, blast furnaces and coke batteries be excluded from an ongoing job boycott, after ArcelorMittal argued these are essential services barred from striking by law, NUMSA said.
"Justice Mahosi of the labour court interdicted the strike temporarily but only for workers in the blast furnaces, coke batteries and the steel plant, until a final judgment has been made," NUMSA said in a statement.
The union wants a 10% pay increase, a housing allowance and payment of 80% of medical insurance costs, against the company's final offer of a 7% wage increase.
ArcelorMittal was not available to comment.
A NUMSA spokesperson said she could not immediately establish how many of union members worked in the departments affected by the court order but said NUMSA was the biggest union at ArcelorMittal, with about half of the company's permanent employees affiliated to it.
The company, majority owned by Luxembourg-based ArcelorMittal SA, had 7,133 permanent workers at the end of 2021, its latest annual report showed.
On Thursday, scores of striking workers picketed outside ArcelorMittal's Vereeniging plant about 100 kilometres south of Johannesburg, chanting protest songs, burning tyres and blocking roads with cement blocks and debris as police kept a close watch.
"We want a 10% salary increase, that's why we are standing outside," Marake Mokoena, a crane driver, told Reuters.
"This is because (the price of) everything is increasing, petrol, food and everything, but the company doesn't want to give us that percentage, so we will fight until we get that 10% increase."
(Reporting by Nelson Banya; editing by Jason Neely and David Evans)