Thousands of protesters are expected to march in French cities, while public sector workers stage a nationwide strike against rising living costs, conditions in education and problems in public services.
The protests present another challenge for President Emmanuel Macron, after weeks of unrest that have shaken his government. The mobilization is organized by trade unions and is also supported by student groups.
French authorities have deployed around 70,000 police officers to ensure security, while between 500,000 and 700,000 people are expected to take part in demonstrations outside Paris.
The strike is expected to cause disruptions in schools, public transport and rail services. The energy sector has also been affected, with nuclear output down by 2.4 gigawatts.
Students are expected to join the protests, raising concerns about conditions in schools and uncertainty over their future.