Motorists using the Dartford River Crossing could have to pay more money as part of plans to tackle congestion.
Dart-Tag drivers would not see a rise in daytime charges
The proposals, announced by the Transport Minister Stephen Ladyman, would see night-time charges scrapped.
However, daytime charges would be increased from £1 to £1.50, with a 50p discount for drivers opting to use the pre-paid electronic Dart-Tag system.
But Kent County Council and Labour MP for Dartford Dr Howard Stoate have condemned the plans.
Keith Ferrin, the council's cabinet member for highways, said a 50p increase would be "totally outrageous" and said the council would fight the increased charges.
He said drivers were already being penalised with little benefit for Kent.
"To ramp up the daily charge by another 50p would add insult to injury... It represents a 50% increase over a year. They [the government] are squeezing the motorist even more."
Dr Stoate said that, as ministers had refused to ring-fence the income from tolls for local transport projects, he could not accept these changes or the continued use of the tolls.
He said a consultation with local residents showed that 45% of them believed all tolls should be abolished.
"Local residents are unhappy that they have to continue to pay to use the crossing when so little of the revenue from tolls is spent on transport projects in Dartford."
Geoff Dossetter, from the Freight Transport Association, said tolls should have been scrapped when they paid for the construction costs of the crossing four years ago.
He added: "The price increases seem to be a half-baked attempt at road pricing, but will surely do nothing to reduce traffic volumes."
Dr Ladyman said action was needed given the volume of traffic and long queues.
"As traffic increases the queues will get worse, so we need to act," he said.
The minister said the removal of night-time charges, when traffic is much lighter, was in line with "our desire to see more freight moving at night when the roads are less congested".
There will also be a new study looking at the capacity of traffic over the River Thames to the east of London.
Dr Ladyman said it would look at how to address the pressures in the longer term, including the possibility of a new crossing.
The Dart-Tag is a small electronic device that is attached to the windscreen and registers when users have incurred a charge.
Motorists put credit on the cards before making their journeys, thus reducing congestion at the toll booths.