Twenty-six people have been arrested in Gauteng for intimidation, public violence and malicious damage to property as police monitor the metals and engineering strike, police said on Friday.
The 26 were arrested in connection with crimes committed over the past three days, Lt-Col Lungelo Dlamini said.
Of these, 19 people were arrested in Elandsfontein on the East Rand after protesters, believed to be strikers in the metals and engineering industries, broke the gate of a business.
When police arrived, the crowd stoned their vehicles. Police used rubber bullets to disperse them.
In a separate incident in Benoni on Thursday, around 2000 striking workers forced their way into a company and damaged equipment and computers. The damage was estimated at several million rand.
In Wadeville, also on the East Rand, nine people were arrested for allegedly breaking windows at a business premises.
"Although it is a protected strike and employees are allowed to picket, acts of violence will not be tolerated and police are ready to take action," Dlamini said.
Majority union in the metals and engineering industries, the National Union of Metalworkers of SA (Numsa) embarked on an indefinite strike on Tuesday. Several smaller unions have joined the strike.
Numsa is demanding a one-year bargaining agreement, including a 15 percent wage increase, a R1000 housing allowance, and the scrapping of labour brokers.
On Thursday, the biggest employers' organisation, the Steel and Engineering Industries Federation of SA (Seifsa), tabled a three-year wage offer of between eight and 10 percent for different levels of workers in the first year.
The first category of worker was offered seven percent in 2015 and 2016, while the others were offered nine percent in the second year, and eight percent in the final year.
The National Employers' Association of SA (Neasa) has offered eight percent, subject to an agreement for entry-level workers' wages to be lowered and measures to make the industry more flexible.
Neasa CEO Gerhard Papenfus said the employers' demand relating to entry-level wages was aimed at boosting job creation.
He said around half of companies affected by the strike had reported violence and intimidation.
Seifsa also complained that some of their members had reported damage to property and violence accompanying the strike.
The federation's CEO Kaizer Nyatsumba has written to national police commissioner Riah Phiyega twice, calling on police to prepare for a potentially violent strike.
Phiyega's spokesman Lt-Gen Solomon Makgale confirmed on Friday that the letters had been received.
"The law makes provision for protest but clearly stipulates that such protest cannot be violent," he said.
Seifsa has expressed concern that Numsa refused to sign a peace accord, and the matter has been referred to the Commission for Conciliation, Mediation and Arbitration.
Numsa was not available for comment on Friday.
In a statement on Thursday, however, spokesman Castro Ngobese denied Numsa members were behind the crimes.
"Numsa condemns the spurious accusations being made by employers that our striking members are involved in acts of intimidation and vandalism."
Responding to Seifsa's letters to Phiyega, Ngobese said the union rejected this as an attempt to involve organs of state in the strike.
"Seifsa should not open unhealed wounds. Workers have not forgotten their comrades were slaughtered in Marikana by the police," he said in a statement at the time.
On August 16, 2012, 34 people, mostly striking mineworkers, were shot dead at Lonmin's platinum mining operations in Marikana, North West, in a clash with police. Police were apparently trying to disarm and disperse them.
Earlier on Friday, the SA Chamber of Commerce and Industry condemned strike-related violence and called on the police to arrest the perpetrators.
"The high economic costs and severe infringement on the rights of South African citizens indicate that government must intervene to avert anarchy," CEO Neren Rau said in a statement.
Communications Minister Faith Muthambi said in a statement that the government condemned the violence attributed to Numsa members.
"Whilst South Africans have the constitutional right to protest, intimidation and violence against those not participating in the strike will not be accepted," she said.
"South Africa is a democratic country where concerns ought to be addressed within the framework of the law."
The government called on employers and trade unions to work together to reach an amicable and speedy resolution.
Labour Minister Mildred Oliphant is expected to meet Seifsa and Numsa later on Friday, following her meeting with Numsa on Monday, spokesman Mokgadi Pela said.