Three drivers were caught using red diesel in their vehicles when police and other agencies teamed up for an operation.
Officers from the Outer West Leeds team and colleagues checked 40 vehicles in the Thornbury area during Operation Dodgegill.
The drivers were issued with fines topping £1,000.
Police also received a lead on a farm possibly selling red diesel, which is being pursued by HRMC.
PCSO Muen Muftee, who arranged the operation, said: “This was a very productive day which saw some really good results. I’m really pleased we have the opportunity to work alongside our partner agencies.
“Customs guidelines state red diesel can be used for home or business heating or to power off road farm vehicles and machinery. That is why it is taxed much less heavily.
“Motorists who do not pay the fines face having their vehicles impounded.”
Taxi licensing checks led to one driver being suspended, and another driver was told to get an MOT inspection.
The checks also uncovered a Transit fan carrying passengers without a seatbelt, for which the driver received a £100 fine and three penalty points.
Officers issued a driver £100 fine and three points for carrying passengers in a Transit van with no fitted seats.
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