The National Union of Metalworkers of South Africa (Numsa) has called a one-day strike for Wednesday to highlight youth unemployment in the country, where one in four people are jobless, the union said.
The 340 000-member union draws its members from car manufacturing, the metal industry, transport and general workers.
The strike would be the latest in a string of work stoppages.
“It is a strike that members in all other unions can join. We think half a million workers will take part,” Karl Cloete, deputy general secretary of Numsa, told Reuters on Sunday.
In December, Numsa, the biggest bloc in the Cosatu, said it would not support the ANC in the upcoming election.
Many South Africans are disgruntled by the slow pace at which the ANC is rolling back poverty two decades after the end of apartheid.
A strike over wages in the platinum sector has been going on for nearly two months and has cost employees more than R3.8bn ($354m) in lost earnings.
The strike has cost mining companies R8.6bn in revenue so far, according to a tally updated almost every second on the Chamber of Mines’ website.