Tolls on the Dartford Crossing are set to rise by up to 30% in October, with another increase scheduled for 2014.
The government has announced that the charge on the M25's Dartford-Thurrock crossing will go up from £1.50 to £2.00 this autumn for cars, from £2.00 to £2.50 for light goods vehicles, and from £3.70 to £5.00 for heavy goods vehicles.
When electronic charging is introduced in 2014, the tolls will then rise to £2.50 for cars, £3.00 for light goods vehicles and £6.00 for heavy goods vehicles.
Announcing the new charges, Road Minister Mike Penning said work was continuing on analysing options for a new Lower Thames crossing.
He said: "The Dartford-Thurrock River Crossing is a vital piece of transport infrastructure that has brought huge economic benefits to the country.
"But currently it can't meet the growing demands of drivers so we need to plan properly for the longer term."
AA president Edmund King described the price rise, the first since November 2008, as "totally unacceptable".
He added: "Drivers have paid for this crossing many times over and hence all tolls should be dropped.
"It is ludicrous to argue that tolls are in place to manage demand - drivers on the M25 do not have the luxury of choosing another crossing and therefore the crossing has a captive market."