Campaigners against plans to sell-off the Dartford Crossing have protested on the Kent side of the River Thames.
The previous Labour government announced it could be sold to a private company which would collect the tolls.
The plans are expected to be raised again in the coalition government's budget next Tuesday.
Protesters say the crossing should have been free to use after 2003, when building costs were met, and they feared tolls would stay if it was sold.
Campaigner James Willis said, even though there had been a change of government, protesters wanted to get the message across that Dartford residents and motorists were "absolutely outraged" at the sell-off plans.
"If the crossing's sold, the toll will never go," he said, adding that in the long run the campaign was to abolish the toll completely.
Gareth Johnson, the Conservative MP for Dartford, who is also opposed to the sell-off, said the ultimate goal was to scrap the tolls.
He said: "The first battle that we have to win is to persuade George Osborne in Tuesday's budget not to announce the sale of the Dartford Crossing."
Mr Johnson said that, while understanding the attraction in keeping the tolls because they provided £42m in revenue to the government, it actually cost the country money to keep the tolls.
He said: "We lose out on business, investment and trade in the local area.
"The Dartford Crossing could actually open up the Thames Gateway area.
"It really could be a positive thing for the area, but it's not.
"It actually restricts and holds back Dartford, and therefore consequently costs the whole area a lot more than the £42m."
A spokesman for the Treasury said it was not possible to pre-empt the contents of next week's budget.