PARIS — Firing an employee in France often means a court date, months of hearings and hefty payouts under the country’s 3,400-page labor code. Employers hate the thick book.  But workers — those lucky enough to have jobs — love it. On Wednesday, thousands went into the streets across France to protect it, demonstrating against a new government plan to make firings slightly easier and France’s trademark shortened workweek slightly longer.  Nothing for years has so revived labor tensions — or divided the Socialist Party — as the government’s plan to overhaul the voluminous labor code, removing, ever so slightly, a few layers of worker protection.  Desperate to reduce a nearly permanent unemployment rate of more than 10 percent, the Socialist prime minister, Manuel Valls, has risked taking a delicate paring knife to the labor code, a step that members of his party consider a heresy.  In doing so, Mr. Valls and his tiny reform faction have revived a conflict over labor overhauls that has already played out elsewhere in Europe’s left, but that has tormented the French Socialists ever since they took power in 2012.  Mr. Valls says he is determined to fix a “broken” French system that has left employers so fearful of long-term hires that 90 percent of jobs created in France last year were unstable, poorly paid and short term.  “You engage yourself practically for life when you sign a contract,” said François Asselin, a businessman who heads the confederation of small- and medium-size companies in France.  “When you want to lay off an employee, there is considerable legal and financial risk,” he said. “In France, to lay someone off, you’ve got to be totally documented, so you won’t be accused of an ‘abusive firing.’ ”  Mr. Valls’s departures from leftist orthodoxy, however, run the risk of breaking his own Socialist Party.  “Why are they doing this one year away” from the election, lamented Catherine Lemorton, a Socialist parliamentary deputy, in an interview on Wednesday. “This law which offends so much of our electorate, or what’s left of it?”  Mr. Valls, pugnacious and combative, boxes in his spare time, and the law was introduced with characteristic brusqueness and little explanation. The reaction has been explosive.  For weeks the Socialist Party’s rank and file has cried betrayal. Hundreds of thousands have signed an online petition demanding that the government scrap its plan.  Deputies in Parliament have revolted. The unions — “it’s a return to the 19th century,” grumbled one leader — have vowed to kill the plan.  One of the leading Socialist lights, the mayor of Lille, Martine Aubry, who wrote France’s 35-hour workweek as a government minister, wrote a furious editorial in Le Monde, declaring, “Not this, not us, not the Left!”  On Wednesday, as the government hunkered down to ponder its dwindling options, thousands of demonstrators — workers, union officials, students — poured into the streets of the country’s cities.  The student mobilization against the plan was especially strong.  “That kind of society, we don’t want anything to do it!” read one of the student demonstration banners at the Place de la République in Paris.  This baffled government officials, who said the plan had been developed with students in mind, to open up more long-term employment and diminish exploitative short-term jobs.  “They want to make us Kleenex employees, throwaway employees!” said Patricia Deschamp, an Air France worker handing out leaflets at the big demonstration near the employers’ federation here on the Left Bank.  “We have minimal security now, and we will have even less after,” she said.  Yet the agitated crowds were in the streets for a level of protection far higher than in many developed countries and against a change that even its defenders characterized as no more than mild.  The main provision puts a cap on payouts to laid-off employees, based on seniority. Labor court judges would not have nearly limitless discretion to award huge payouts.  Equally infuriating to the unions, the law defines more precisely when a company can invoke “economic” reasons to justify layoffs. Workers who refuse to go along with temporary workload increases in the event of increased business could be laid off, too.  “It will simplify the procedures to layoffs,” said Philippe Aghion, a Harvard economist who is French and who lectures at the prestigious Collège de France. “You won’t have to go through endless judicial procedures. There will be less discretion for the judges. Now, there is enormous discretion on the amount.”  The uncertainty factor is a killer for hiring, the business owners say. “All we are asking for is a limit on the ceiling,” said Mr. Asselin, whose company is a leader in the restoration of France’s historic buildings.  “Now, there are no limits,” he said. “Sometimes the fines are so big they endanger the employer. So today, it is risky to hire people.”  The unions here, keen to protect their already-employed members, speak relatively little about the ranks of the unemployed. Yet many economists contend that the French level of protection for workers is poisonous to the job market.  “There is a large body of evidence that increasing levels of protection for existing workers is detrimental to the labor market, particularly on weaker categories of workers, the young and women,” said Pierre-Olivier Gourinchas, a French economist who teaches at the University of California, Berkeley.  “If we want to address the fact that it’s a labor market that excludes many, many people from a decent level of job protection by forcing them into short-term jobs, we have to address these conditions,” he said. “The current administration has accepted this perspective.”  France, however, is a difficult country to reform, as Mr. Aghion and others pointed out. Cultural shifts like those proposed by the current government always bring people into the streets.  “We are a country of revolutionaries and conservatives at the same time,” said Marc Lazar, a historian at the Institut d’Études Politiques.  Playing into this is the French left’s deep attachment to “advances acquired in the past,” Mr. Lazar said.  The prevailing sentiment is that “you shouldn’t touch the labor code, because we prefer equality to liberty, protection to adventure.”  A version of this article appears in print on March 10, 2016, on page A6 of the New York edition with the headline: French Premier, Trying to Make Firing Easier, Risks His Own Job . Order Reprints| Today's Paper|Subscribe
Thousands marched in Paris on Wednesday to protest proposals that would make it easier to fire workers, but that the government says could mean more jobs.