A prosecution against Maidenhead Wine Company Ltd from Cordwallis Street was launched by the Royal Borough trading standards department after the vehicle was stopped on the Bath Road in November during a joint operation with police.
It was weighed and found to be 1,120kgs above its maximum legal limit of 3,500kgs.
Two extra vans were needed to off-load enough cargo - mostly cases of wine - to bring its weight in line with the legislation.
The Royal Borough said overloading can affect brakes, steering and put other drivers and road users at risk.
The company admitted guilty by post to overloading a vehicle under the Road Traffic Act.
It was fined £1,700 and told to pay £1,013 costs during a hearing at Slough Magistrates' Court on Thursday.
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