JOHANNESBURG (Reuters) – Workers downed tools Monday at three South African power stations with more set to follow as a wage strike began at state-run utility Eskom, but the company said its operations had not yet been impacted and branded the stoppage illegal.

Paris Mashego, NUM’s energy sector coordinator, told Reuters that wage talks with the utility were in deadlock over the weekend. Eskom provides almost all the power to Africa’s most industrialised economy but it was not immediately clear what impact the strike may have on its ability to keep the lights on.

An Eskom spokesman said operations had not yet been impacted and reiterated the utility’s view that its members are prohibited by law from striking.

“Across all of our 27 power stations everything is operating as normal at this stage,” spokesman Khulu Phasiwe said.

“And no one from Eskom is allowed to go on strike because we are defined as essential service providers. Technically anyone who is not at work today will have to explain themselves to their bosses,” he said.

He added that Eskom did not feel that negotiations had collapsed. The utility is offering pay hikes of 7 to 9 percent while NUM is looking for increases ranging from 12 to 13 percent.

Phasiwe also said NUM members early on Monday morning had blocked roads leading to the Arnot power station east of Johannesburg but police had been called in and the roads were now clear.

NUM has around 15,000 members at Eskom, close to a third of its workforce.

The stoppage coincides with a wage strike by around 15,000 workers in the petrochemical industry that has led to some shortages and was entering its second week on Monday.

(Reporting by Ed Stoddard; Editing by James Macharia)