Eurotunnel is advising all passengers booked on day trips to France to postpone their journey if possible.
It is offering refunds to anyone booked on a day return who is able to postpone their trip.
The warning comes after further delays caused by migrant activity at Calais.
Earlier today (Tuesday) timetables were disrupted with only up to three departures per hour.
A later Twitter post from the operator said services were delayed by 30 minutes at both Folkstone and Calais.
"We’re all working to reduce them. Thank you for your patience," it added.
Eurotunnel also warned of traffic congestion in Kent and asked customers to tweet it with their experiences so it could monitor traffic conditions.
"If you’re travelling to our UK terminal today, please tweet how long Operation Stack diversions took so we can inform other customers," it posted.
