This week the country's National Assembly voted to extend it by six months.
The vote followed last week's Bastille Day lorry attack by Mohamed Lahouaiej Bouhlel, who left 84 people dead when he drove through crowds on Nice's Promenade des Anglais.
A Port of Dover spokesman said: "Due to ongoing heightened French security checks, the Port of Dover is advising customers to allow plenty of time for their journey.
“Local traffic may wish to consider using alternative routes where possible to avoid queuing traffic."