Santander has been accused of misleading customers about their rights following the spectacular collapse of Monarch Airlines.
More than 860,000 people in the UK have been affected by the failure of the airline, with more than 100,000 stranded abroad.
Some, who bought an ATOL-protected holidays, will be able to reclaim their money from the body. Meanwhile, of those who aren't eligible, many should be entitled to a refund from their bank.
However, dozens of frustrated passengers have been complaining on Twitter that they have been wrongly turned away.
Under Section 75 of the Consumer Credit Act, those who paid between £100 and £30,000 by credit card should be able to claw the money back from their credit card provider.
In most cases, they will need to have booked direct with the tour operator or airline, although some credit card companies will give a refund even if you've paid via a travel agent.
Meanwhile, those who paid via debit card after 15 December last year should be able to claim the money back from their bank under a voluntary chargeback scheme.
"Santander's refusing to refund under sec 75 people who've lost money on Monarch flights bought after 15/12/16," writes one Twitter user, with another saying: "Santander will not refund debit cards at the moment as cannot reclaim money back from Monarch!"
Santander is now telling customers to call on 0800 9123 123 to discuss their situation.
"We apologise if staff have provided wrong information at any point," a spokesperson tells the Sun.
"Our call centres and branches have all been briefed on what our position is and this was put in to place as quickly as possible once Monarch's situation was confirmed this morning."
Barclays Bank is also telling customers to contact Monarch first, as it will only issue refunds if the airline won't.
"If Monarch are unable to help you, please contact us to raise a dispute," it says. "If you've booked using your Barclaycard, please contact them directly."