Striking power workers put the lights out in Johannesburg, South Africa, for three days last week.
Some 200 technicians walked out unofficially over shift changes. Bosses claimed some workers with technical know-how shut down sub stations, causing blackouts.
Johannesburg mayor Parks Tau is threatening criminal charges, saying there could not have been blackouts without sabotage.
However the workers have been ordered to do the extra shifts because they had not been able to halt earlier power cuts working their existing hours.
Workers in the motor, construction and gold industries have all recently held strikes over wage demands across the country.