Police are cracking down on cars with ultra-dark window tinting, as it has become clear too many people are unaware there is a legal limit.

Senior Sergeant Dale Johnson said police would be testing cars to check whether their window tint was impeding the driver's vision and complied with Victorian road laws.

Cars are deemed unroadworthy if its windows transmit less than 70 per cent of visible light. Credit:Leanne Pickett

"We've detected far too many vehicles with tints as low as 3 per cent. The legal tint is 35 per cent or higher," he said.

"If you're getting your windows tinted, make sure to ask the light transmittance percentage and if you doubt the legality of your tint, get it checked."