The SA Municipal Workers' Union was stopped from participating in the nationwide public service strike, the City of Johannesburg says.
"The interdict was granted by Justice la Grange in the Johannesburg Labour Court," spokesman Gabu Tugwana said in a statement.
"Samwu or city employees who consider strike action must show cause why the order cannot be made final by 8 September."
Tugwana said the order meant that any strike action by city employees would be unlawful. Any worker who went on strike could face disciplinary action and possible dismissal.