Eastern Cape emergency medical services workers are demanding outstanding overtime pay.
Some workers claim they have not been paid their overtime pay since 2003, GroundUp reports.
They embarked on a strike on Monday, which has been declared unlawful by officials who have promised to take disciplinary action against employees who participated in it.
"We are disappointed that the workers have embarked on an illegal strike knowing that they are employed as essential services and therefore are not to be on strike. The department will undertake internal processes for on duty employees involved in this illegal strike," Eastern Cape health MEC Helen August-Sauls said.
She said her department was busy processing overtime payments from 2015 to 2018.
An ambulance driver who has been employed for nearly 10 years said they were working under stressful conditions.
The driver, who did not want to be named, said employees were often met with a hostile reception in communities where they were blamed for arriving late to help patients.
"This should be blamed on government that has very few ambulances and is understaffed. We are overwhelmed by calls and we end up working overtime."
He said the department had promised to pay overtime "but nothing has materialised".
Another employee who also requested anonymity said he was owed "a lot of money for the past two years".
The department said private ambulances would be used to respond to life-threatening cases during the strike.
Ambulances in parts of the Eastern Cape are notorious for the amount of time they take to arrive.
In 2013, according to NSP Spotlight, residents of Xhora lodged a complaint with the Human Rights Commission about the tardy ambulance service.
In 2017, GroundUp published a story of a Mooiplaas resident who was attacked and injured. Eventually, five hours after calling an ambulance, the person had to be taken to hospital in a private vehicle.