France was set for a fresh day of protests over labour reforms on Thursday, in yet another challenge for the embattled government of President François Hollande. The protests led by student groups and labour unions coincide with strikes by air traffic controllers that are expected to cause travel chaos for thousands of passengers. A few moderate unions have given their support to proposed changes to France's famously stringent labour laws, but tens of thousands of people have taken to the streets in the past three weeks, angry over plans to make it easier for companies to fire workers. Marches have turned violent at times, with cars burned and more than 30 people arrested in Paris last week. A video of an officer punching a 15-year-old boy being held by two other officers on the sidelines of a protest in the capital went viral and has fuelled further anger. Organisers have threatened an even bigger day of demonstrations on Thursday. Protesters were set to start gathering at Place d'Italie in southern Paris around 1pm. Socialists divided A battle is also raging within Hollande's ruling Socialist party, with many on the left of the party fiercely opposed to the reforms, billed as a last-gasp attempt to boost France's flailing economy before next year's presidential election. Hollande has vowed not to run again if he cannot put a dent in the country's stubbornly high unemployment figures – long stuck at around 10 percent – and hoped the modest labour reforms would encourage firms to hire more people. But pressure from the street and parliament's back benches caused the government to water down the proposals so that they only apply to large firms. A recent poll found that 58 percent of the French public still opposed the measures. Labour Minister Myriam El Khomri said this week that she understood why "such a profoundly reformist text has raised questions and requires debate", adding that "it is not a blank cheque for companies". Bosses are also unhappy, particularly over the removal of a cap on compensation paid for unfair dismissal, and the scrapping of plans that would have allowed small- and medium-sized companies to unilaterally introduce flexible working hours. Parliament is set to vote on the reforms in late April or early May. Lack of authority Meanwhile, aviation authorities told airlines to cancel 20 percent of their flights from Paris Orly airport on Thursday and a third of flights from Marseille, as air traffic controllers went on strike again. Paris Charles De Gaulle airport was not expected to be affected by the 36-hour walkout over job cuts and the lack of investment in new technology. A strike last week disrupted travel plans for thousands of passengers as airlines were forced to cancel up to a third of flights. Regional train services in France will be running a half service on Thursday as rail workers join the nationwide strikes against the disputed labour reforms. The demonstrations are another challenge to Hollande's authority, who was still stinging from his government's failure to introduce a constitutional reform he claimed would help authorities fight the threat of terror. Hollande on Wednesday scrapped the constitutional reforms he proposed following the Paris attacks, including a plan to strip convicted terrorists of French nationality. In a blow to his faltering credibility, Hollande said an agreement between the two houses of parliament on the measures had proved impossible.