Farmers said the protests, now in their second week after breaking out in the southwest, would continue as long as their demands are not met, posing the first big challenge for new Prime Minister Gabriel Attal.
As Attal convened senior ministers, farmers used bales of hay and tractors to block major arteries across the country, the European Union's biggest agricultural producer.
Crates of tomatoes, cabbages and cauliflowers that one group of farmers said had been imported from neighbouring countries were strewn across the A7 highway that links Marseille and Lyon, France's second and third biggest cities.
Some farming unions have threatened to blockade Paris. On Thursday, dozens of tractors led a go-slow during rush-hour near Versailles on the southwestern edge of the capital.
The powerful FNSEA farming union late on Wednesday handed the government a list of 100 demands.
Yohann Barbe, FNSEA spokesman, told RMC radio the demands revolved around "helping farmers regain their dignity, their ability to earn a living income, and above all putting an end to the overload of regulations".
Farmers cite a government tax on tractor fuel, cheap imports, water storage issues, price pressures from retailers and red tape and environmental rules among their grievances.
Farmer discontent over price levels is particularly acute in the dairy sector, where producers say the government's anti-inflation push has undermined legislation designed to safeguard farmgate prices.
French retailers are locked in annual price negotiations with suppliers, which the government wants concluded by the end of the month. Farmers say they will be on the sharp end of efforts to haul prices lower.
Fearing a spillover from farmer unrest in Germany, Poland and Romania, the French government has already postponed a draft farming law meant to help more people become farmers, saying it will beef up the measures and ease some regulations.
Ahead of European Parliament elections in June, President Emmanuel Macron is wary that farmers are a growing constituency for the far right.
Far right leader Marine Le Pen accused the government of complacency and backing European regulations that hurt farmers, such as rules on mandatory fallow land.
"Emmanuel Macron addresses farmers with a hand on the shoulder and then knifes them in the back in Brussels," Le Pen told reporters.
Farmers in the southwest who on Wednesday sprayed liquid manure over a local prefecture building in Agen, on Thursday directed their animal waste at a nearby Leclerc superstore, France's biggest supermarket chain, as police looked on.
