PARIS - A labor strike in France, prompted by concerns over Britain's withdrawal from the European Union, might spread to the flying public. Strikes by customs agents at ports and rail stations earlier in the week could now spread airports.

Long lines of trucks at Calais and Dunkirk ports. Two-hour delays for Britain-bound Eurostar rail passengers. That was the scene this week in France for passengers and merchandise headed for the U.K. French customs agents staged slowdowns by strictly observing rules, leading to lengthy security checks, a preview, they claim, of what might happen if Britain leaves the European Union without an exit agreement later this month.

Unions warned select French airports would also be affected over the weekend, including the country’s busiest hub, Charles de Gaulle, outside Paris — amid heavy school holiday traffic.

Christophe Abadie, head of the (CFDT) customs labor union, urged passengers to prepare for potential delays. He told France’s CNews TV that the French customs service lacks the technical and infrastructure ability to deal with Brexit. The government says it will be recruiting 700 more agents to cope with Brexit demands. Unions say that’s not enough. They also want better pay and working conditions.

Another customs union member warned that without enough reinforcements, kilometer-long lines seen this week at northern French ports could be even longer under a no-deal Brexit. French authorities say they’ll be prepared. The minister in charge of customs, Gerald Darmanin, meets with union leaders early next week.

British lawmakers are set to vote again Tuesday on Prime Minister Theresa May’s Brexit deal, and reports suggest its passage is unlikely. Like France, other European countries are concerned about the transportation chaos that could result from London’s departure from the EU without an agreement.

That’s especially true for the Netherlands, where authorities at Europe’s largest port of Rotterdam warned last month that a no-deal Brexit could lead to serious problems. A Dutch transportation institute also warned that under a worst-case Brexit scenario, trade between Britain and the Netherlands could drop by as much as 50 percent.