ABUJA (Reuters) - The Nigerian National Petroleum Corporation (NNPC) has fired 850 workers, many of them 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), speaking 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. Nigeria is dependent on crude sales to prop up its struggling economy, now at risk of its worst recession in four decades due to the coronavirus and the pandemic tanking global oil prices.

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.