Tens of thousands of Spanish lorry drivers have begun an indefinite strike over the soaring price of diesel, which has risen by 20% this year.
After stopping work at midnight, many disrupted traffic at one of the border crossings between Spain and France.
French fishermen from Mediterranean ports have, meanwhile, joined fleets from other French ports in suspending their action pending an EU summit in Brussels later this month.
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Overnight, about 200 lorry drivers parked their vehicles beside roadside toll booths in the Catalonian town of La Jonquera, close to the border with France.
The protesters prevented other lorries from passing, and caused delays to car traffic.
Hundreds of lorry drivers also staged "snail protests" on the ring roads around the capital, Madrid, and Barcelona. There have also been protests in the Basque country and Valencia.
Most of the 90,000 hauliers participating in the strike are self-employed, or working for small and medium-sized haulage companies, and they have warned that many supermarkets will run out of goods within days. Petrol supplies may also be disrupted.
We are the ones who move the goods that this country needs to keep working," the head of the transport association federation Fenadismer, Julio Villascusa, told Cadena SER radio.
"If we stop because we haven't got the money to buy fuel then the country will stop."
The president of another drivers' trade union, Adetec, said many of its small-scale hauliers were going bankrupt.
"We have no more solutions. We can't afford diesel any more. It's as simple as that," Jean-Claude Ferrand told Spanish national radio.
The lorry drivers are receiving support from counterparts in Portugal and southern France, who also disrupted the flow of traffic along one of the main routes into Spain.
Their strike follows action by hauliers in France and other European countries. They are following the lead of Spanish and French fishermen, many of whom have been on strike because of the soaring price of fuel.
The fishermen have said they will go out of business unless the EU allows national governments to give them more financial aid and subsidise maritime diesel.
However, the EU has insisted that any fuel subsidies would be illegal under European law and unsustainable in the long term.
EU rules state that the value-added tax (VAT) rate on fuel cannot be less than 15%. Member states are free to set VAT rates at or above that minimum.