A French labour union said members working in the energy sector had on Thursday cut power to the building sites for the Olympic Village for the 2024 Paris Games, as well as the main Stade de France stadium.
Gas and electricity supplies were cut to the sites as well as data centres, said Sebastien Menesplier, secretary general of the hardline CGT union's energy branch, as unions step up actions to thwart the government's controversial pension reform.
Unions are keeping up actions to force the government to drop the plan, with transport and other public services disrupted in France for the third day in a row.
The government under President Emmanuel Macron says raising the retirement age from 62 to 64 and stiffening the requirements for a full pension are essential to keep the system from sinking into deficit.
"Faced with a government that refuses to budge, we too are refusing to budge," said Menesplier.
"I appeal to the responsibility of the government and the president of the republic: withdraw your reform and the electricians and the gas workers will work for the public service and the general interest", he added.
About three hundred employees were present for the action which saw them tamper with four key cables. Some, hooded, raised their arms and lit smoke bombs to hide those who cut the power from the cameras.
The electricity supplier then sought to work rapidly remotely to restore supplies to the affected areas.
Strikers in the energy sector have since Tuesday staged wildcat power cuts, plunging certain sites across the country into darkness.
Government spokesman Olivier Veran on Wednesday condemned the wildcat cuts while expressing respect for the right to express disagreement in the street.
"We condemn calls to bring our economy to its knees because this is irresponsible. The only thing we want to bring to its knees is unemployment," he added.
The government late on Wednesday passed a major legislative hurdle for its bill when the upper house Senate, dominated by the opposition right, gave its approval to the article on raising the retirement age.