The London Evening Standard reports that the scam is said to based on tax relief for bogus charitable donations.
A fraud investigation team from the Inland Revenue questioned the workers about the scam which has allegedly been running for some while.
The sum involved could be as much as £2 million.
It came to light after the Inland Revenue began investigations into certain aspects of allegations of racial harassment and bullying by production line employees last year.
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Five million taxpayers are ow using digital personal tax accounts (PTA) as part of the making tax digital strategy, HMRC said