The Nigerian National Petroleum Corporation (NNPC) has sacked 850 workers. Many of the affceted staff from refineries, amidst the coronavirus pandemic, an oil union said on Tuesday.

The workers are both skilled and unskilled contractors, including technicians who helped maintain Nigeria’s oil refineries, said Lumumba Okugbawa, general secretary of the Petroleum and Natural Gas Senior Staff Association of Nigeria (PENGASSAN), told Reuters on the phone.

The NNPC did not immediately respond to requests for comment. Layoffs in Nigeria’s oil sector are a tense issue, with frequent stand-offs between the NNPC and unions.

Yet Nigeria’s refineries are barely operational. Almost all of the country’s fuel supply is processed overseas at great cost, despite Nigeria being Africa’s largest crude producer.

In May, the NNPC said it had more than 6,600 staff.