Angry NatWest customers vented their frustrations through the night as they reported being unable to use their debit cards in shops and having their PINs blocked.
People who faced the problem took to the bank's Twitter and Facebook pages from around 11am on New Year's Day to say their cards were being declined.
Many said they had issues making purchases at various supermarkets, including branches of Tesco.
At 11.16am Jake Orr tweeted: "@NatWest_Help Just had my pin locked when trying to buy food. Shop says all Natwest card users getting the same this morning. Update?"
Around 12 hours later, the problem continued, with NatWest responding to customers, tweeting: "Hi there, we're aware of some issues using Debit Cards and we are working hard to fix them. Sorry and thanks for your patience."
Throughout the day angry NatWest debit card holders used Twitter to attack the service.
Michael E Morley posted: "What a let down! Card useless this morning reimburse us our money your helpline cost too much and it's your fault not happy!"
Fiona Davis tweeted: "Embarrassing issue with both our cards blocked when trying to pay for goods at Tesco. Not a good start to New Year!"
Shaun Kirkpatrick shared similar feelings, posting: "Thanks for causing me embarrassment when doing my food shop ... Just what you want with a queue of people behind you!"
Other NatWest cardholders said the latest glitch had made them consider switching banks.
Joanne Clark wrote on Facebook: "What a lovely start to the new year! I'm a proud customer of yours since I was 14 (I'm now 28) and needed to go shopping! Usually my husband doesn't bring his wallet out thank god today on the off chance he did!
"You see I had an embarrassing moment when I got to the checkout with my £50 worth of shopping for my card to be declined claiming I had tried my pin too many times and to contact yourselves!
With two young kids playing me up and me panicking as we were far from home and nothing in the cupboards!
"I've never been more tempted in my life to go elsewhere, what with last year the great direct debits not being taken twice as your systems went down!! This is so irritating!!!!
"At least message or email customers when you know of this like you do when charges are due!!!"
Responding to the complaints, NatWest tweeted: "We're aware of some issues with customers using their debit cards and are working hard to fix them. Sorry and thanks for your patience."
A spokeswoman for Royal Bank of Scotland-owned NatWest added that the issue was affecting a "very small number of customers" attempting to carry out point of sale transactions with debit cards and apologised for the inconvenience.
In June last year RBS was forced to apologise after 600,000 banking payments were delayed following an issue with its "overnight process".
It was just another in a string of embarrassing IT glitches to hit NatWest and RBS in recent years.
In 2013, RBS's online service was disrupted by a denial-of-service attack.
In November 2014, the state-backed group was hit with a £56 million fine from the Bank of England and City watchdog Financial Conduct Authority (FCA) after a computer failure in 2012 saw as many as 6.5 million customers unable to make payments for as long as three weeks.