Public consultation has begun on changes to toll charges at the Dartford River Crossing between Kent and Essex.
The bridge and tunnels take M25 traffic over and under the Thames
The government is proposing an increase in daytime charges, but at a reduced rate for electronic DART-Tag users. Night charges would be removed.
The plans are aimed at reducing congestion at the bridge and tunnels, but three MPs have tabled a motion in Parliament for them to be dropped.
People can have their say in the consultation until 9 March.
Views can be expressed on the Department for Transport website, or documents are available from the offices of Dartford Borough Council and Thurrock Council.
PROPOSED TOLL CHANGES
Cars - day charges up from £1 to £1.50
2-axle goods vehicle - day charges up from £1.80 to £2
Multi-axle goods vehicle - day charges up from £2.90 to £4
DART-Tag cars - 93p to £1
DART-Tag 2-axle goods - £1.67 to £1.75
DART-Tag multi-axle goods - £2.69 to £3.20
All night-time charges would be scrapped
Daytime is 0600-2200 GMT, night-time is 2200-0600 GMT
Essex MPs Bob Russell (Lib Dem) and Bob Spink (Tory), and Hertfordshire MP Mike Penning (Tory), have called for all tolls to be completely scrapped.
They have pointed out that the charges were set to be withdrawn when the crossing had paid for itself, which in fact happened in 2003.
But the government said the tolls were continuing as a safety measure, in order to control the flow of traffic.
The National Alliance Against Tolls argued: "US research shows that approaches to tolls are the most dangerous places on the road."
The group cited drivers slowing down, searching for change or switching lanes as potential dangers.
Transport Minister Stephen Ladyman said of the proposed toll changes: "Without intervention now, traffic levels will continue to grow."
The government said an average of 150,000 vehicles a day used the crossing in 2005 (combined average for north and southbound traffic).