“The violence is unacceptable,” said Interior Minister Bernard Cazeneuve, noting that police had arrested 62 people across the country, 32 of whom were kept in custody.

Authorities said some 78,000 people rallied overall nationwide, including 13,000 in Paris. Organisers put numbers across France at around 170,000, saying 40,000 protested in Paris.

The law aimed at loosening France’s notoriously rigid employment laws was forced through in July after months of often violent protests. In all 620 police have been injured since the protests started, said Cazeneuve.

It notably makes it easier to fire workers during downturns and for bosses to negotiate directly with employees on working time.

As well as the protests, scores of flights in and out of the country were also cancelled as air traffic controllers went on strike to protest the law.

“We will show them that, law or no law, we will always stand against them,” said Francois Roche, a member of the hardline CGT union demonstrating in Marseille.

Turnout nationwide was far lower than at the first rallies earlier this year which saw hundreds of thousands of people take to the streets.

One of the focal points Thursday was the eastern city of Belfort, where the government is locked in a battle with train-building giant Alstom over the future of a locomotive factory threatened with closure.

Hundreds of demonstrators marched through the city, chanting “Alstom is Belfort, Belfort is Alstom”.

Belfort’s history is intertwined with that of Alstom, which produced its first steam train there in 1880. The plant now assembles high-speed TGV train locomotives.

Last week, Alstom had announced it would close the plant due to a lack of orders and move production to a site 200 kilometres to the north.

The prospect of up to 400 job losses is deeply embarrassing for the Socialist government eight months ahead of presidential and parliamentary elections, in which high unemployment is expected to be a key issue.

Aviation authorities had advised airlines serving Paris airports to cancel 15 per cent of their flights Thursday over the air traffic controllers strike.

Low-cost airline Ryanair said it had cancelled scores of flights to or through France.

The new labour law - one of the few major reforms of President Francois Hollande’s tenure - aims to bring down France’s unemployment rate of around 10 percent.

Opponents, however, see the measures as an erosion of workers’ hard-won collective bargaining rights.

Such was the opposition to the changes on the left, including from within the Socialists’ own ranks, the government had to force through the bill without a vote, causing a deep divide within the ruling party.

“The biggest loser from this law is Francois Hollande,” Jean-Claude Mailly, leader of Force Ouvriere trade union, said Thursday.

The violence unleashed by the reforms peaked on June 14, just four days after the start of the Euro 2016 football championships in France, when around 40 people were hurt and dozens arrested.

CGT leader Philippe Martinez has appealed to workers to continue “fighting tooth and nail to stop it (the law) crossing the threshold” of their companies.

Hollande, who has yet to announce whether he will seek re-election next year, had hoped for a signature reform to boost his dire approval ratings.

Currently, around four out of five French voters oppose him standing for a second term.