London mayor Ken Livingstone said last week it was likely that the £8 charge for entering the congestion zone in central London would rise to £10 in 2008.
A spokesman for the Forum of Private Business said increasing the charge would have a damaging impact on retailers. He added: "This is just another tax on retailers. The government is hitting them to pay for its own inefficiencies at local and national level."
Geoff Dossetter of the Freight Transport Association added: "Any hike would increase costs to customers. Administration alone would add millions in costs for the industry."
A spokesman for the London Retail Consortium said: "It is clear that no economic impact analysis has been undertaken to look at the effect that such an increase in the Congestion Charge would have on London retailers."