The "Yellow Vests" protests, which have taken motorists' safety jackets as their symbol, were first suggested by individuals claiming to be apolitical on Facebook and other social media.
They blame increases in an environmental tax for the rise in petrol and diesel, although the government says that is mainly due to world oil markets.
The call for action has received a particularly big response in small towns and rural areas, whose inhabitants complain that public transport and other services are poor to non-existent and cars a necessity for daily life.
It has also given voice to wider concerns over the government's policies, perceived as favouring the wealthy and big-city dwellers, and against allegedly heavy taxation.
Mixed messages from government
The government has stuck to its guns on the tax rises, while promising measures to ease the burden on people on low incomes and to help them buy less-polluting vehicles.
But it has sent out mixed messages as to how it will react to disruption caused by the movement.
"People can demonstrate but blockading a country when the emergency services need to circulate, when anybody may need to travel tomorrow, is obviously not acceptable," commented Prime Minister Edouard Philippe on Friday.
Along with Environment Minister François de Rugy, he was on a visit whose subject seemed specially chosen for the occasion - a site where cars are tested for conformity to European Union directives, especially in relation to pollution.
With bus drivers in the Normandy city of Rouen declaring solidarity with the protests by placing yellow jackets on their dashboards and reports that police officers backed the movement, Transport Minister Elisabeth Borne reminded public employees that they must respect the principle of neutrality while at work.
She also highlighted the authorities' problems in knowing how many demonstrations will take place, where they will be and how many people will be on them.
"A lot of demonstrations have been announced but very few have been declared," she told CNews TV.
French law requires protest organisers to notify the authorities 72 hours ahead of the event.
Trade unions, political parties and other long-established organisations usually comply with the law and organise stewarding.
But these protests are being organised by inexperienced individuals who may not even know about their legal responsibilities.
That leaves police in front of a dilemma as to how tough to be with unauthorised events, especially since their may be families on them.
Two women who called the protest in the south-western city of Tarbes called it off on Thursday after police and intelligence agents warned them they could heavy fines or imprisonment if there is damage to property.
That earned them denunciations as sell-outs and collaborators on Facebook.
Thirty additional police units are to be on standby to intervene if needed on Saturday.
Left accused of hypocrisy
Opposition parties and trade unions have also been caught off-guard by the movement.
The government has accused left-wingers, such as the France Unbowed party and the Greens, of contradicting their commitment to the environment by backing the protests.
De Rugy brandished an amendment calling for a rise of 500 million euros in carbon tax before France Unbowed MP Clémentine Autain in parliament, pointing to her signature in second place.
"We don't want the ecological transition to be paid for by people who are struggling to keep their heads above water but first of all by big business, in particular the motorway operators," she replied.
"Macronism is using the environmental cause as an alibi to justify its inaction on social questions," leading Green Yannick Jadot said.
The Socialist Party has also said it would stand by people "defending their standard of living".
Far right enthusiastic
Laurent Wauquiez of the mainstream-right Republicans accused the government not listening to the people and announced he would join in a protest in his constituency.
Marine Le Pen's National Rally (previously the National Front) has been even more enthusiastic, leading to accusations that the movement is being exploited by the far right.
Le Pen herself has said she would not take part in a demonstration but that many of the party's elected representatives and other activists would.
That has led Philippe Martinez, the head of the left-wing CGT trade union, to declare that it was "impossible" for his organisation to "march alongside the National Front".
He also accused "big bosses" of hijacking the movement as part of a campaign against taxes and social security contributions and called for pay rises rather than tax cuts.
The two biggest farmers' unions have supported the movement, although the left-wing Confédération Paysanne echoed Martinez's claim that it has been hijacked by the far right, while expressing sympathy for the "anger of the people that will be expressed on 17 November.