"It was symbolic," Solidarity union spokesman Jaco Kleynhans said.
The Solidarity trade union was hosting a briefing on its possible class action suit against troubled state utility Eskom over job cuts when it was reminded of South Africa's power woes.
Delegates were left in the dark when Eskom implemented its daily blackouts that have caused traffic chaos and darkened homes.
South Africans are seething over a power crisis the government has warned could take years to resolve.
Eskom produces about 95 percent of South Africa's electricity and is spending billions of dollars to expand its generating capacity as it struggles to cope with rising demand from the country's growing economy.