Thousands of protesters marched under tight security in eastern Paris on Saturday after French labor unions, left-wing political parties and civil rights groups called for "floods of people" to oppose the pro-business policies of President Emmanuel Macron.
Marches and rallies also were being held in dozens of other French cities as part of the joint action against Macron's policies that organizers consider imbalanced and "brutal."
At the Paris event, Philippe Martinez, head of leading French union CGT, advised the president to "look out the window of his palace to see real life."
Police estimated that 21,000 people took part in the Paris protest, while CGT put the number at 80,000.
More than 1,500 police officers were mobilized in the French capital to prevent activists not associated with the official protest from disrupting the march and causing damage, which has happened during recent demonstrations.
Police said they detained 39 people in Paris before and after the march started, including 26 who were put into custody. Most of them were preemptively taken in for questioning after officers searched their bags and found what they described as equipment that could be used to cause damage or to hide faces.
Others, mainly youths dressed in black with their faces covered, were detained on the sidelines of the main protest for breaking windows at a business or damaging bus shelters. Police used tear gas canisters to push them back. One officer was slightly injured by thrown debris.
Unions, opposition parties and other groups are particularly denouncing a Macron-led legal overhaul aimed at cutting worker protections and increasing police powers.
They allege that Macron supports tax reform that favors France's wealthiest and is working to tear down public services. They also oppose a government plan making it harder for students to attend the public universities of their choice, more restrictive immigration laws and police methods in underprivileged neighborhoods that protesters consider "repressive."
In the southern port city of Marseille, Jean-Luc Melenchon, leader of the far-left Defiant France party, also addressed Macron while speaking to demonstrators.
"In the name of the poor, the humiliated, the homeless and the jobless, we are telling you, 'Enough, enough of this world,'" Melenchon said.
Macron, a centrist former investment banker, says his economic changes are meant to increase France's global competitiveness. In an interview with BFM TV on Friday, the French leader said that those who protest will not manage to "block the country."
"No disorder will stop me, and calm will return," Macron said.
4:05 p.m.: This article was updated with estimates on the number of protesters.