The operators of the privately-run Highway 25 toll bridge are being threatened with a class action lawsuit.

Lawyers say tens of thousands of people are being overcharged because the sign isn't clear enough about the cost to use the bridge.

There are signs for drivers approaching the Olivier Charbonneau bridge, including one with a digital display where the prices, which alter depending on time of day, are shown.

But lawyers say that sign is five kilometres from the bridge and is not clear.

Jamie Benizri of the firm Legal Logic represents the lead complainant in the case, a Laval resident who claims the sign is misleading because it does not explain the higher cost to cross during rush hours.

"The bottom line is you're basically getting an estimate on that billboard 5 kilometres before the ramp. By the time you get to the ramp the estimate that you got in money surged, goes up without any warning, any indication, so it's actually false advertising," said Benizri.

This case has yet to be approved by a judge, a necessary step before it moves forward.

The company that operates the bridge had no comment when contacted by CTV.

The Olivier Charbonneau Bridge opened in 2011 and it is the first in Quebec to use an exclusively electronic payment system: the licence place of each vehicle is recorded a a bill sent in the mail, or drivers can use pre-installed transponders and save money.

The bridge operators were sued before by the Union des Consommateurs about the extra fee that was charged to drivers who did not have transponders.

That case was settled out of court for $4.8 million.