Last month's electricity blackout hurt 82 per cent of small businesses in Ontario and cost the provincial economy between $1bn and $2bn, said the Canadian Federation of Independent Business (CFIB).
The small-business group said its survey of Ontario members found 47 per cent shut down completely because of the power failure and 35 per cent endured a partial shutdown.
More than one-quarter of the 1,935 small businesses responding to the poll said they cut back production and one-sixth asked some or all of their employees to stay at home.
Seven per cent lost inventory because of inadequate refrigeration or delayed transport.
Two per cent reported vandalism costs or heightened security expenses while the lights were out.
Companies with five or fewer employees reported blackout-related losses averaging $780 per worker - almost double the $400 per employee reported by larger enterprises.
