The supermarket giant issues Clubcard vouchers in February, May, August and November.
All vouchers have a two-year lifespan before they expire.
Millions of customers have been contacted by Tesco to inform them that vouchers sent in August 2021 will expire next month, on August 31.
An email to customers said: “You have Clubcard vouchers that are about to expire.”
Every £1 spent in Tesco stores or online is worth one Clubcard point, with each Clubcard point essentially being worth 1p.
After you collect 150 Clubcard points you can exchange them for a £1.50 voucher or carry on saving points and collect vouchers at 50p intervals from there.
In the past you could also decide to triple the value of your Clubcard points by using them with a “Rewards Partner”, which include Pizza Express, Disney+, Hotels.com and more.
However, the system was changed in June, meaning shoppers are only able to double their points rather than triple them.
A Tesco spokesperson said: “Clubcard unlocks the best value from Tesco – from thousands of exclusive deals through Clubcard Prices, to money off your groceries and fuel, or accessing double the value of your vouchers with more than 100 Clubcard Reward Partners.
“Millions of people tap their Tesco Clubcard every time they shop, benefiting from access to more than 8,000 weekly deals on Clubcard Prices.
“And with potential savings of up to £351 a year, more people than ever before are making the most of the immediate value that Tesco Clubcard offers.
“We are making a change to how members can use their vouchers with our Reward Partners, but they will still be able to unlock great value in the same range of ways as before.”