Paul Everitt, SMMT chief executive, said: “This is totally disproportionate and does not present a consistent signal to consumers.
"The mayor has made it clear that charges will be varied in future and has not clarified the period in which discounts will apply.
"We can be confident that this means higher charges and the gradual erosion of discounts for band A and B cars. I shall therefore be writing to the mayor seeking a three-year application period before any further changes are made to the scheme."
Everitt stated that while the SMMT does supports the mayor's stated aim to reduce congestion, independent reports suggest the changes could encourage between 4,000-10,000 additional cars onto central London roads. That could mean more congestion and delays for drivers within the zone.