South African police have fired tear gas after clashes between opposition supporters and trade union activists.
Opposition leader Helen Zille told the BBC that about 1,000 unionists attacked her supporters in central Johannesburg.
The Cosatu trade union federation regretted the violence and said its members were also wounded.
Ms Zille's Democratic Alliance organised the march to support a government policy of subsidising the wages of young workers.
The DA says this will lead to the creation of abut 400,000 jobs in the country, where about half of young people cannot find work.
But Cosatu says the "Youth Wage Subsidy" will lower wages for everyone and could mean older people being sacked to make way for younger, cheaper workers.
The violence broke out when hundreds of DA supporters wearing blue T-shirts reached Cosatu headquarters, where they were met by unionists clad in red.
Ms Zille denied that the march was provocative and said it was fully authorised.
"There is nothing provocative about people exercising their constitutional rights to peaceful protest," she told the BBC's Focus on Africa programme.
She also accused the police of withdrawing "leaving our marchers at the mercy of Cosatu", which she said was "wholly unacceptable".
The DA leader said she would study video of the violence to determine who had incited the violence.
The DA is South Africa's second largest party, behind the ANC, which has governed the country since the end of white minority rule in 1994.