The U.S. Federal Energy Regulatory Commission judge said the companies responsible included Powerex, a wholly owned subsidiary of BC Hydro.
California’s chaotic summer of 2000 saw waves of rolling blackouts and sky- high electricity prices and the state's Public Utilities Commission has long claimed that companies like Powerex manipulated the market for record profits.
"It's an extraordinarily important case for California and a big victory really for the consumers in California,” said Frank Lindh, the commission’s general counsel.
The judge's initial decision, released this week, cited some 20,000 violations and affects about a dozen companies. But Lindh said Powerex and Canadian firm TransAlta were among the biggest players.
If the commission accepts the ruling, as Lindh told CBC News he expects will happen, the companies will owe Californians $1 billion in refunds, plus $600 million interest.
About 30 other companies have settled for $3 billion so far, Lindh said.
BC Hydro was unavailable for comment Wednesday night.
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