Johannesburg, South Africa – Around 220,000 engineering and metal workers belonging to South Africa’s biggest trade union have launched an indefinite strike over wages.

Members of the National Union of Metalworkers of South Africa (NUMSA), the country’s largest labour union, said they would not relent on their demand for a 15 percent wage increase. On Tuesday, NUMSA and other smaller unions marched in several cities, including Johannesburg, Cape Town and Durban. Though there were no reports of violence, there were incidents of vandalism and complaints of intimidation.

Once a stanch ally of the ANC ruling party, NUMSA withdrew support for Jacob Zuma’s party during the presidential elections in May, arguing for a new party dedicated to the poor. The strike came just days after workers in the platinum mine industry ended a five month strike where NUMSA sent a message of congratulations to the “courageous mineworkers for securing a decisive and historic settlement in the platinum belt”.

“This settlement is not only a victory for mineworkers, but for workers in South Africa as a whole,” the statement read.