Louder and louder, the crowd chanted: “Macron! You’re screwed! The slackers have taken to the streets!” The protesters had gathered in the Place de la Bastille in Paris on 12 September for the first in a series of marches to oppose President Emmanuel Macron’s attempt to liberalise the French labour market.

In the capital, as well as in Marseilles, Lyon, Toulouse, Rennes and other cities, several hundred thousand people attended the demonstrations called by the General Confederation of Labour (CGT), one of the biggest French unions. Two more nationwide protests occurred on 21 and 23 September.

A few days before the first march, Macron had caused widespread offence by declaring his “absolute determination” not to “cede any ground to the slackers, the cynics, the extreme”.

“Who is the president talking about? The millions of people in precarious jobs or without one?” the CGT’s leader, Philippe Martinez, asked the press. An editorial in the Libération newspaper said: “If he was looking to get as many people as possible to protest, Emmanuel Macron would not have acted differently.”

At the Paris march, the word “slacker” was alluded to on placards (“Too lazy to find a slogan”) and was on many of the protesters’ minds. “His generalised contempt, it’s unbearable,” the 19-year-old philosophy student Marius Jouanny said.

Last year, François Hollande’s attempt to reform France’s labour code also drew big protests and led to the French Occupy, “Nuit debout” (“Up all night”). But Hollande’s law, which made working hours more flexible and was forced through by his government, was modest compared to Macron’s. His plans will make it easier to lay people off, permit employers to bypass unions in certain negotiations and allow much more flexible contracts with employees. Macron says the reforms are needed to make the French economy more competitive, attract investors and reduce the country’s stubbornly high unemployment rate of 9.5 per cent, which is above the eurozone average.

The unions have called the proposals “labour law XXL”. Jean-Luc Mélenchon, the leader of the far-left party France Insoumise (“Untamed France”), described them as a “social coup d’état”. Critics say that Macron’s reforms will significantly reduce job security. Currently, employers cannot fire someone without proving “professional fault” on the employee’s part and must comply with numerous regulations that protect his or her rights.

“This is not a labour law. It’s one that gives full powers to the employers,” the CGT’s Martinez said.

The labour reforms are the first real test for Macron, whose approval ratings have collapsed from 66 per cent after his election in May to 30 per cent in early September. This followed Macron’s decision to reduce housing aid and to push through the new labour law via government rulings, without a vote, despite his party’s parliamentary majority.

In an attempt to avoid a rerun of the protests that greeted Hollande’s labour laws – Macron was economy minister at the time – the new president made a deal with the other big workers’ unions, which did not call for their members to demonstrate. But several of their local branches took part in the march in Paris.

“Entire sections of the labour code are in danger,” the 42-year-old Frédéric Dorléac, from the Seine-et-Marne branch of the Working Force (FO) union, told me. “They are Uberising workers.” José Carrique, 59, a CGT representative and an electricity worker, said: “It’s a total liberalisation of working hours, conditions, salaries. Look at Germany’s day contracts, at the British zero-hours contract. Soon French workers will be the same. They will not work to live any more, but live to work.”

Socialists, including the party’s presidential candidate, Benoît Hamon, have expressed support for the protests. Marine Le Pen’s Front National condemned the law without joining in the demonstrations.

Mélenchon, who came fourth in the presidential election with 20 per cent of the vote, attended the march in his constituency of Marseilles. “The government can and will back off,” he told French TV. “We will be implacable and protect the labour code. This country doesn’t want a liberal market. France is not the UK.”

At the Paris protest, Mélenchon’s supporters hung France Insoumise posters on trees along the Boulevard de la Bastille. As he marched past an improvised stand selling second-hand books (sections included “history and revolutions” and “unions and business”), Samy Ghribi, a 24-year-old web developer, said that Macron’s government was “too liberal”. “They take money from people who need it,” he added, citing the cuts to housing aid and the plans to lower the rate of the “wealth tax” levied on the richest.

Many workers fear that the new laws will hit their pockets and extend their working hours. Leyla, a nurse’s aide who requested that only her first name be used, said her hourly wage and time off would fall. “Nurses already don’t have enough time to rest. We can’t work properly.” Sylvain, 30, a maintenance worker at Disneyland, said his bosses had started testing new flexible-hours contracts. “We’ll come in the morning without knowing how long we’ll work for. We have lives!” he added.

Joël, a 57-year-old CGT representative and former Total employee, said he feared the loss of the workers’ protections that his parents and grandparents had fought for: “It’s all going up in smoke. We get that France needs economic growth, but it cannot always be to the detriment of the workers.”

In the sea of protesters in Paris during the first big demonstration, one sign stood out. “The king sucks” – a reference to Macron. It did not help that the “king” was away, visiting the victims of Hurricane Irma in the French Caribbean. To his detractors, he was avoiding his first serious day of discontent at home. As he extends his plans for reforms in other areas – pensions, rail and unemployment benefits – it is unlikely to be his last.