The new measures have been introduced to prevent fraud, and mean that your card will be declined if you use contactless five times in a row.
At this point, you'll be prompted to put your card into the machine and use your pin.
Your card will also be blocked from working contactlessly if you spend £137, even if that's in fewer than five transactions.
You are also more likely to have your card stopped if you are shopping in an unusual location.
The new rules were introduced back in September, which means you could be affected when you're doing your Christmas shopping.
Christo Georgiev, chief executive of UK payment solutions company myPOS, warned that customers need to have their PIN handy this festive period, even when paying for low-value items.
He said: “You shouldn’t panic when your card is declined once the limit has been reached, just continue using your card but make sure you can enter your PIN to complete the transaction.”
The new regulations do not apply to Google Pay or Apple Pay, so you will continue to be able to use these methods as per normal.
How to protect yourself from fraudsters
ACTION Fraud recommends taking the following advice to stay safe:
Shopping online is going to get more complicated too, as you will have to use text authentication to prove that its you who is shopping.
Text authentication is being phased in, but retailers must comply by March 2021 at the latest.
But experts are concerned about what this measure could mean for customers than don't use a mobile phone.
On top of that, lots of banks haven't yet made alternative arrangements for customers with poor phone signal.
Email delays may also mean that shoppers don't receive the codes before the transaction has timed out.
And anyone relying on generated card readers will have to keep them on hand at all times.
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