An exclusive Fleet News' survey, carried out in conjunction with Calor Autogas, revealed that more than a third of fleets questioned said their companies would be affected by the charge, which is introduced in February.
More than 430 companies were interviewed for the survey, with fleet sizes ranging from less than 10 vehicles to more than 1,000.
Results showed that 35% thought the charge would have an impact on their businesses, with one firm claiming there would be a £100,000 cost per year and another fearing a £30,000 a year charge.
One company said it may have to relocate its headquarters out of London, while another said it may avoid serving clients in the congestion charging zone.
Several companies surveyed said they would have to pass the cost of the charges on to customers, or suffer reduced profit margins.
Yet despite the massive disruption involved, the survey showed only 16% of companies ran LPG vehicles, which receive a 100% discount from the charge if they meet stringent emission standards. Less than 40% of companies were aware of the LPG discount and 62% said they would now consider converting or may consider converting in future.
Key barriers to change were the current ban on LPG vehicles travelling in the Channel Tunnel, the patchy refuelling network and uncertainty over the future tax treatment of the fuel. The report was revealed as London's Lord Mayor, Gavyn Arthur, warned hundreds of thousands of jobs could be lost because companies were considering relocating abroad as a direct result of Britain's transport problems.