Internet bank Egg could face questions from the Office of Fair Trading (OFT) over allegations it cancelled some of its customers' cards because they paid their balance in full each month.
The credit card provider wrote to more than 160,000 customers in January of this year to inform them their accounts were being cancelled due to the level of their "risk profile".
Some of those affected have claimed, however, that far from being 'risky' customers they have instead pay their balance in full each month - something they claim makes them less profitable as credit card customers.
A complaint from MP and former consumer affairs minister Nigel Griffiths has now been passed to the regulator by the Financial Services Authority.
The OFT has yet to decide whether it will launch a formal investigation into the claims. A spokesperson for Egg said that the card cancellations were made following a "one-off review" which found that some customers "presented a higher than acceptable credit risk to the bank".