PARIS, France (AFP) — French riot police fired teargas and stun grenades Thursday during clashes in Paris with opponents of labour reforms who threw molotov cocktails in the latest outbreak of violence over the controversial new laws.

At least four demonstrators and eight police were injured – including one officer who sustained burns – as tens of thousands rallied against the law, forced through by the Socialist government in July after months of often violent protests.

At least 15 people were arrested in the capital, where police said around 13,000 people took part in the rally against measures aimed at loosening France’s notoriously rigid employment laws – the 14th such demonstration in six months.

A march in the western city of Nantes also turned violent, with police there using tear gas and water cannon against protesters.

Nationwide, around 78,000 took part in the protests, according to the police. The organisers estimated the turnout at around 170,000.

Scores of flights in and out of the country were also cancelled as air traffic controllers went on strike to protest the law that makes it easier to fire workers during downturns and for bosses to negotiate directly with employees on working time.

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

The turnout nationwide was however far lower than at the start of the rallies six months ago, when they brought hundreds of thousands of people onto 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 (120 miles) 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 percent 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.