Another Border Force strike taking place 15 March could become much worse than planned for travellers.
It coincides with another round of France strikes as protests over pensions continue.
“This industrial action may lead to additional disruption at French ports not due to Border Force strike action,” the UK government said.
It cautions travellers to prepare for longer wait times at border control.
“Always check with your operator before you travel and follow their advice.”
Tomorrow is the eighth day of strikes in France
Previous strikes have caused significant disruption on rail, metro and air travel.
Eurostar pro-actively canceled a number of services for earlier this week.
An extended walkout by refuse collectors has left mountains of trash uncollected across Paris.
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