Petrol shortages caused long tailbacks of motorists in parts of France on Monday as protesters angry over government labour reforms blockaded some of the country's oil refineries and fuel depots.
The action was the latest in three months of strikes and protests against the reform, which has set the Socialist government against some of its traditional supporters and sometimes sparked violence.
Workers downed tools at six of France's eight refineries on Monday, the CGT union said.
Prime Minister Manuel Valls denounced what he called trade union "blackmail" and urged the French people "not to succumb to panic" over fears that petrol supplies would dry up, assuring that the depots would be "unblocked".
The northwest of the country was worst hit at the weekend, with riot police dispersing protesters at some fuel depots.
The situation was exacerbated by some motorists rushing to stock up fearing that supplies were about to run out.
"Talking about a shortage creates the shortage," said Finance Minister Michel Sapin.
Local authorities in some areas imposed rationing, as the employers' federation Medef called on the government to "re-establish the rule of law".
- Tailbacks and burning tyres -
The government of embattled President Francois Hollande -- who is deeply unpopular and faces re-election next year -- said the situation had improved since Sunday when 1,500 of the country's 12,000 petrol stations had run dry, but did not have fresh figures.
The Total group said 509 of its 2,200 stations had either run out or were suffering shortages Monday, up from 390 the previous day.
The French authorities said the overall situation was "stable or slightly worse" than Sunday.
Tailbacks slowed traffic, particularly in the northwest, where motorists waited for up to an hour to get to the pumps at some filling stations.
Originally concentrated in northwest France, the protest action has spread south.
t Fos-sur-Mer, near the Mediterranean port of Marseille, about 500 union activists closed a road leading to a fuel depot with burning tyres. Another road to the nearby refinery was also blocked.
And in Donges, near Nantes on the northwest coast, union activists used wooden pallets and burning tyres to block access to a fuel depot.
Some drivers were hopping across the border into Belgium to fill up their cars
"We are in the front line of this conflict. Without petrol we can't work," said Amazigh, a 24-year-old lorry driver, who was filling his tank in the Belgian border town of Tournai.
- 'French people held hostage' -
The government, which forced the reform bill through the lower house of parliament earlier this month without a vote, insists it will not back down on the labour reform.
Opponents say the law will erode job security and do little to bring down the unemployment rate, stuck at 10 percent and nearly 25 percent for young people.
The government argues that the new law will make France's notoriously rigid labour market more flexible and create jobs.
Labour Minister Myriam El Khomri, the author of the reform, condemned the blockades Monday.
"I have a hard time accepting that workers are being held hostage, that the French people are being held hostage," she said during a visit to Marseille.
In a gesture to road haulage drivers over the weekend, the government promised that their overtime pay would not be affected by the reform as they had feared.
But another day of strikes and demonstrations against the draft law is planned for Thursday, with ports and trains expected to be also affected.
A further day of action is planned for June 14, right in the middle of the Euro 2016 football tournament which will bring thousands of fans to France.
"If the government does not withdraw its plan... the mobilisation will continue and increase," CGT general secretary Philippe Martinez warned Monday on RTL radio.
However EU Commission chief Jean-Claude Juncker has called the French labour plans "the minimum required".
Finance Minister Michel Sapin condemned the CGT's action, telling French television: "There is a certain point... at which (protest) action becomes illegitimate".
Last week, train drivers and air traffic controllers walked off the job, causing cancellations across the country.
Many of the rallies and demonstrations have ended in confrontation between masked youths and riot police.
Some 350 members of the security forces have been injured in demonstrations since March.
The proposed law now faces a vote in the upper house Senate.