No South African worker could be dismissed for taking part in Wednesday's nationwide protest against the e-tolling system and labour brokers, Cosatu said on Monday.
"The strike is protected... and we have complied with the legal requirements," Congress of SA Trade Unions (Cosatu) Gauteng secretary Dumisani Dakile told reporters in Johannesburg.
"Not a single worker can be threatened with dismissal."
He said the certificate issued by the National Economic Development and Labour Council covered every South African worker, whether or not they were part of Cosatu.
"We are even calling on employers to join the march and not threaten workers."
Cosatu expected at least 100,000 marchers. The major event would take place in Johannesburg's central business district.
Cosatu expected its provincial bodies, essential services workers, Eskom workers, teachers, pupils, and other unions to join the strike.
The minimum essential service level would be ensured as per agreements made, said Dakile.
Four marches are planned for the Eastern Cape in Port Elizabeth, East London, Queenstown and Mthatha.