Major disruption is expected today around Calais as hauliers and unionists protest against the migrant camp in the French port.
Vehicles have set out from Dunkirk and Boulogne on the A16 motorway leading to Calais on a "go slow".
The Foreign and Commonwealth Office warned there may be limited access to the Eurotunnel and "significant disruption" to access on the A16 motorway around Calais.
Drivers want the camp known as the "jungle" dismantled and claim they are receving increasing threats from gangs and migrants who are using more dangerous methods in an attempt to reach the UK.
Road Haulage Association chief executive Richard Burnett said: "It seems certain that traffic crossing from the UK will find it almost impossible to leave the port as access to the A16 is denied.
"The inevitable repercussions of this will surely mean that the authorities on this side of the Channel will have no alternative but to deploy Operation Stack.
"This will bring yet further misery to hauliers bound for mainland Europe and of course for the people and businesses of Kent," he said.
There are a reported 80 lorries and 100 tractors taking part in the protest.