A man holds a bouquet of flowers and a torch as he faces riot police during a May 26 demonstration against the government's planned labor reforms. (Jean-Philippe Ksiazek/AFP/Getty Images)

France’s government vowed not to back down from planned labor reforms as union-led protesters in Paris and other cities attempted Thursday to choke off fuel supplies by marching and blocking highways with burning tires.

Seventy-seven people were arrested across France, according to the Interior Ministry, which said more than 150,000 marched. For the past two months, hundreds of thousands have marched against the government’s plans to make it easier for companies to hire and fire.

Organizers plan another day of protests on June 14, four days after the start of the Euro 2016 soccer tournament in France. The General Confederation of Labor (CGT) , a prominent French union and a major organizer of the protests, warned that the tournament could be disrupted if the government refuses to withdraw the draft reform bill that passed the lower house of Parliament this month. It moves to the French Senate on June 13.

The protests are among the most severe since the famous student upheavals of 1968, and they represent not just a mass rejection of a specific policy but unhappiness with a government increasingly viewed — by both the right and the left — as incompetent.

With approval ratings below 20 percent, François Hollande is the most unpopular president in modern French history.

A cloud of black smoke from burning tires billows as two union activists walk toward the Normandie Bridge outside of Le Havre, western France, during a blockade action on May 26. (Raphael Satter/AP)

One year before France’s presidential election, the labor law has become the most fraught chapter in his presidency, raising the rare possibility that he may not be chosen to run for reelection next year.

Labor reforms and the inevitable protests that follow, often with theatrical flare, are common fixtures of French public life. But what makes these different is an underlying sense of betrayal.

“It’s the first time the left is trying to kill the left in power,” said Gerard Grunberg, a French political analyst and historian.

Leftists, such as the union leaders blockading each of France’s eight oil refineries, are leading the charge against a Socialist government whose platform they view as too similar to that of the right.

They overwhelmingly oppose Hollande’s labor law, which would relax some of France’s famous worker protections — among the strictest in the world — in order to curb unemployment and stimulate economic growth.

“It’s a return to the 19th century,” said Roger Rechsman, 69, a retired police officer who was one of thousands marching Thursday in the protest in Paris’s Place de la Bastille. “And that’s what we call ‘modernity.’ ”

The government has offered no hint of compromise as the country struggles with unemployment over 10 percent, just beneath its all-time high.

“What are the alternatives? A withdrawal of the text? That’s impossible,” Prime Minister Manuel Valls said on RMC radio.

He said some “modifications” could be considered but stood firm on the overall objectives. He also took aim at the labor federation leading the protests, saying that it “does not make the law in this country.”

“There will be no retreat,” Valls said.

The head of the CGT was equally firm. “It’s inadmissible,” Arnaud Pacot told BFM television at a nuclear plant occupied by workers.

French workers have prevailed before. Similar protests in the mid-1990s successfully halted a government plan to cut the French pension system in an effort to curb its budget deficit.

Fuel shortages because of the protests have created huge lines at gas stations. The unions also have called for nationwide strikes in the public transportation sector, including air traffic controllers, and at many of the 19 nuclear plants that provide electricity for much of the country.

Brian Murphy in Washington contributed to this report.