France's main trucking union has called on its members to join nationwide strikes to protest against a pension overhaul.
The call ramps up the risk that President Nicolas Sarkozy's flagship reform will be derailed.
An official at the CFDT union said the strike call had been approved at a meeting late yesterday and that the action could start immediately.
Protests by truck drivers, who can block off major roads and access to key sites such as food warehouses, have crippled France's infrastructure in the past and forced governments to cave in on unpopular measures.
'We need those people who are able to make the government understand we won't accept any old thing to come out and do something,' Maxime Dumont, secretary general of the CFDT's trucking branch, told France Info radio.
French unions have meanwhile called a strike for 19 October, to add to protests and industrial action over pension reform that shut refineries, halted trains and brought tens of thousands onto the streets.
Students waving banners critical of President Nicolas Sarkozy demonstrated in several cities yesterday against reforms.
They say the reforms will worsen youth unemployment, however the government says they are vital to reorder a system losing billions of euro a year.
Mr Sarkozy's government has weathered five waves of strike action since June against its plan to raise the retirement age.
Analysts say the dispute may be near a cross-roads as unions attempt lengthier strikes and try for broader social support.
The first four strike waves involved 24-hour stoppages but the latest one has been prolonged since Tuesday as some unions go more radical.
