MONTREAL - Driver beware: those crossing the new A-25 electronic toll bridge should keep an eye on their bills.

Certain types of cars have antennas that can interfere with the transmission of a special transponder that allows subscribers to get lower rates. The transponder is a mechanism that drivers affix to their windshields that transmits information to a receiver.

Cars that do not have the special bridge subscription pay a considerably higher fee.

"I haven't seen an issue when a transponder itself wasn't functioning," said Sam Norouzi, a supervisor on the bridge.

"It has always been an issue with a remote-started antenna, a remote-starter integrated in the windshield, a metalized windshield or a heated windshield that blocks the signal."

Giovanni Raitano noticed the bridge administrators were billing him for those higher fees even though he had shelled out for the special $50 fee (plus $2.50 per month) to pay $1.80 per crossing during the day and $2.40 during rush hour.

His Nissan Sentra apparently contains an antenna that interferes with the signal required to sense his subscription.

Raitano noticed that he was paying the price on his bill and fears many others might have also been overcharged.

"I know it's a small amount," said Raitano. "It's only a $3 surcharge, but multiply it by a couple of times and then the people who don't check their bills. I ask them why and they said it's because I have a Nissan Sentra."

He'll get a refund and keep a keen eye on his bill in the future. He recommends others do as well.

Nearly 30,000 people use the bridge daily, 85 per cent of cars crossing the bridge use a transponder. Toll collection started in May 2011.