Tesco said it has "simplified" its Clubcard rewards scheme to make it more straightforward to use amid criticism that customers will gain less from their points and were given no prior warning.
The UK's largest retailer has written to its millions of Clubcard holders telling them that it will offer three times the value of their vouchers with more than 100 scheme partners as the standard offer.
It is ending those which offered twice the value and four times the value, including some of the most popular deals such as meals at Pizza Express, Prezzo and Zizzi.
A Tesco spokeswoman said: "We've listened to our customers and simplified our Clubcard Reward Partners so that they're more straightforward for everyone.
"This means that from January 15, we will offer customers three times the value of their vouchers with over 100 Clubcard Reward Partners including days out, weekend breaks, holidays and more.
"This builds on the work we did last year to further help customers, when we introduced the new contactless Clubcard and made significant improvements to the Tesco Clubcard app."
Tesco has around 16 million active Clubcard customers, according to figures released at its half-year results announcement.
One customer wrote on Twitter: "We had £89 saved up in vouchers - worth £356. Now they are worth £267.
"No advance warning, really really poor from @Tesco #tescoclubcard - been loyal Tesco customers for well over 10 years - because of clubcard. And what a load of BS about 'making it easier'."
Another wrote: "All clubcard boosts going to 3x. Everything we chose was 4x so this is a big reduction. But highlight was the inane corporate-speak lathered over the announcement...'this is not a reduction in boosts, oh no, this is TO MAKE IT EASIER FOR YOU TO UNDERSTAND' How dumb are we?"
Anika Newjoto, the editor of website shopperpoints.co.uk, said Tesco's move devalued the scheme and did not give customers time to spend their saved vouchers at the old rates.
She said only a small number of Clubcard partners gave twice the face value of vouchers, including National Express, redspottedhanky and Megabus, which are all now going up to three times face value.
She said: "Loyalty schemes are meant to work two ways, not one way.
"If a shopper gives their business to a store based on the promise of certain rewards, it is totally unfair for those rewards to be taken away or reduced in value with absolutely no notice."