Marks & Spencer has denied that its new credit card is in breach of banking regulations.
Store cards are under the spotlight
The company is currently offering 2.6m of its store card holders a new credit card, which has a lower interest rate and more loyalty incentives.
The Banking Code forbids lenders from sending credit cards to people who haven't asked for them, but M&S, which hopes to join the code next year, says it hasn't done anything wrong.
It says it already has an established credit agreement with its charge card lenders - and it is only sending the credit card to those customers it has checked for "credit worthiness".
About 900,000 people are not being offered the credit card - and will continue to use the old charge card which has a higher interest rate.
M&S has already written to about half of those it believes are eligible for the new card.
Customers have a month to reject the offer before it is automatically sent to them.
They can cancel the card at any time after this period.
The credit card has a lower interest rate of 14.9%, compared with the charge card's 18.9% - and customers can collect loyalty points on all their purchases.
The Treasury Select Committee is currently investigating credit and store cards, following concerns about charges - and high debt levels among UK consumers.
But an M&S spokesman denied the launch of the card, with its additional incentives, was irresponsible in the current climate.
"Rather than creating debt, it will, in effect, take business from other card providers," he said.