Workers have downed tools at the Goodyear tyre factory in Uitenhage, the Congress of SA Trade Unions (Cosatu) said on Tuesday.
"The bosses are arrogantly taking away workers' hard-won benefits without following established rules of engagement, as set out in the Labour Relations Actions (LRA)," said Cosatu regional spokesman Phumzile Nodongwe.
"Clearly, they want to create a state of anarchy and render unions useless. We will never succumb to their union-bashing tactics."
Goodyear spokeswoman Lize Hayward confirmed that some National Union of Metalworkers of SA (Numsa) members were on strike and said the company had was trying to resolve the matter by, among other things, using a third party facilitator.
"We believe that we have made reasonable proposals to address Numsa's demands. Despite this Numsa still selected to go on strike," Hayward said in a statement.
"Goodyear remains committed to work with the union on an appropriate solution." She said production had been negatively impacted by the strike.
The Numsa members embarked on a protected strike demanding a relief allowance when placed on staggered breaks.
They claimed this had always been standard practice within the company.
Cosatu said that although the relief allowance had not been part of the collective bargaining agreement, it had been "willy-nilly parachuted behind the tables" by the employer.
"The employer cannot now hastily renege from this, without following proper channels of engagement with the workers," Nodongwe said.
If the company failed to heed the call it would feel "the wrath of the striking workers until their demand is met".