Fortesqueue's managing director Scott Balfour says: "In the long run we may need to raise our prices." The corporate hospitality provider holds Christmas and summer events at Lincoln's Inn Fields in the heart of the charging zone. "We have up to 50 deliveries daily, as well as caterers, bands and contractors. It all adds up and we could be talking about thousands of pounds in additional costs."
The charge imposed by London mayor Ken Livingstone operates from Monday to Friday and costs £5 a day to drive through the centre of the capital.
North London venue Wembley stands outside the zone, but sales and marketing director Peter Tudor believes the capital as a whole could suffer. "This will be seen as yet another expense of holding an event in London," he said.
Organiser Mind Body Spirit is holding two festivals at Westminster's Royal Horticultural Halls in May and November. Managing director Sharon Adams said: "It could be awkward for exhibitors, but so far it hasn't affected our bookings."
Rene Dee, managing director of the Westminster venue, said most visitors came by public transport but warned that the contracting sector was likely to suffer.
British Exhibition Contractors Association director Lynn Felton said: "It is an amount that contractors will have to find. It's important for them to know exactly where the congestion zone is and how to pay, so they can avoid expensive fines.