Twenty-eight female guards were unfairly dismissed by a security company because the client‚ Metrora.
Four municipal cleaners were assaulted and a security vehicle set alight in Tembisa during a clash between striking and non-striking workers yesterday.
More than 300 contracted waste removal workers have been on strike for the past eight weeks demanding permanent employment by the municipality.
A Citi-Golf belonging to Good Sheppard Security was set alight while it was escorting a truck collecting rubbish in the Emfihlweni section.
Ekurhuleni metro police's Inspector Mveli Ntlapo said: "The group of contract waste removal workers approached the truck and the escort vehicle from different directions.
"They threw stones at the truck before assaulting the four men and setting the escort vehicle alight with petrol."
He said police were also investigating whether the recent torching of a councillor's car and yesterday's violence are linked.
"We are investigating the link between this and the burning of Councillor Zachariah Mpongose's car at the weekend," he said.
Zweli Xaba, chairman of the South African Municipal Workers' Union, blamed the council for "pushing contractors to act the way they do.
"The strike will not stop until the municipality fulfills its promise," he threatened.
Since the strike began in February, six contractors have been shot and injured by metro police after ignoring warning to disperse.
Tembisa police confirmed that a case of malicious damage to property had been opened.