(Bloomberg) -- Mastercard Inc. lost a bid to narrow the size of the UK’s largest ever class action claim over its payment fees after appeal judges rejected its attempt to exclude some 3 million people who died since the claim was first filed.

The credit card provider is facing a claim that’s at least £10 billion ($12 billion) from Walter Merricks, the former head of the UK’s Financial Ombudsman Service representing more than 46 million consumers. The UK courts gave the green light to the suit last year in the first judicial certification of its kind.

Mastercard, which was trying to reduce the size of any potential damages, had argued that the 3 million people who have died since the claim was first issued should be excluded. 

But the Court of Appeal in London on Tuesday ruled that the suit should proceed from the original starting point of 2016. The judges sided with Merricks, who argued that it was only because of the delays to the long-running case that the claimants had died in the meantime.

To exclude those who had died “would be a windfall for Mastercard,” the judges said. “To put the same point another way, the effect of Mastercard’s case would be to thwart, at least to a significant extent, the overall purpose of the regime.”

The case stems from an EU ruling that the interchange card fees the company charged for transactions were unfair and breached of competition law.

“This case isn’t about helping consumers,” Mastercard said. “This flawed claim is being pushed by lawyers and their financial backers primarily focused on making money for themselves, and is likely to take years to conclude. We will continue to fight it and are confident that, once the facts are presented in court, the case will be thrown out.”

Boris Bronfentrinker, a lawyer for Merricks, said the he will now focus on the merits of the case in their pursuit of damages.

(Updates with comment from Merricks lawyer in penultimate paragraph.)

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