France was hit with a wave of power cuts as thousands of workers rallied against the government's plan to raise the retirement age to 64.
Union activists cut electricity to nearly 100,000 homes or offices in Bordeaux and Lyon, while staff at the Eiffel Tower walked off the job.
Even Paris opera workers joined in Tuesday's nationwide protests, singing an aria in protest.
Despite 13 days of crippling train and subway strikes, French president Emmanuel Macron and his government have refused to give in to the worker's demands.
Prime minister Edouard Philippe declared his "total" determination to reshape a pension system which unions celebrate as a model for the rest of the world, but which he calls unfair and destined to collapse into debt.
Lighting red flares and marching beneath a blanket of union flags, thousands of workers snaked through French cities from Brittany on the Atlantic to the Pyrenees in the south.
Hospital workers in scrubs, Air France staff in uniforms and lawyers wearing long black robes joined people from across the French workforce in the strikes and protests in higher numbers than the last cross-sector walkout last week.
The Eiffel Tower was shut for the second time since the strike, one of the most protracted France has seen in years, started on December 5.
Police in Paris barricaded the presidential Elysee Palace, bracing for violence by yellow vest activists or other radical demonstrators.
Across the French capital, union leaders said Mr Macron should drop the retirement reform.
"They should open their eyes," said Philippe Martinez, the head of the CGT union, at the head of the Paris march.
Costume fitter Bernard Buffet, 63, is retiring in April after 35 years at the Bastille Opera.
However, he said he was protesting in solidarity with younger colleagues.
"The government is stuck on the reform. They are very arrogant," he said.
Mr Philippe confirmed new negotiations with unions will start on Wednesday, but showed no sign of backing down.
"Democratic opposition, union opposition is perfectly legitimate," he told MPs. "But we clearly laid out our plans. And on this plan, the creation of a universal retirement system, my determination ... is total."
