Thousands of French energy workers have staged a mass strike, triggering power cuts in some areas.
Unions called the 24-hour stoppage in response to government plans to transform state-owned power firms EDF and GDF into limited companies.
They see the move as a prelude to a full sell-off, despite government promises to hold on to a minimum 70% stake in the utilities.
The strike has curbed energy output, causing blackouts in the Paris suburbs.
Some localised power outages were also reported on the Mediterranean coast.
Short-term electricity prices were sharply higher on the wholesale energy markets in anticipation of shortages.
The leading CGT union claimed a protest march it organised in central Paris had attracted 80,000 people.
Unions said about three quarters of the 150,000 staff at EDF and GDF were observing the strike, although management claimed the figure was closer to 45%.
The strike is the latest in a series of protests against moves to liberalise France's power markets over the last two years.
Unions claim privatising the power utilities would lead to large-scale job losses, and would undermine France's tradition of public service.
They have argued that privatisation could lead to power cuts of the kind that paralysed the US east coast and parts of Italy last summer.
CGT secretary general Frederic Imbrecht told the AFP news agency that the union was planning more strikes and protests at local level in mid-June, when the French assembly is due to debate the proposed change.
Electricity provider EDF has responded with a series of full-page newspaper advertisements claiming that consumers will benefit from the planned change to limited company status.