Inflation-linked price rises for mobile phone contracts and broadband services have been banned, with a new rules laid out for providers.
As of Friday, providers must clearly set out any mid-contract price hikes in pounds and pence.
Regulator Ofcom, which has enforced the changes, said they will protect consumers amid "incredibly volatile" inflation rates.
However, fixed price rises will still be allowed, and critics have labelled it a "transparency tax".
Here, Yahoo News UK explains the changes.
In recent years, many phone, broadband and pay TV providers have included price rises in their contract terms that were linked to unknown future inflation rates. They are now banned from doing this.
Instead, firms must set out any future price hikes "prominently and transparently" in pounds and pence at the point of sale.
This means consumers will now be able to choose a contract featuring clear information ahead of annual price rises in April. The below graphic, from Ofcom, visualises that change.
Ofcom has been investigating mid-contract price rises since 2023. Its analysis found more than half of mobile customers and around four in 10 broadband customers were on inflation-linked contracts in April that year.
Yet a survey found only 16% of these broadband customers and 12% of mobile customers knew their costs could rise.
Meanwhile, these inflation-based rises often included an extra percentage increase on top, making it near impossible for consumers to accurately estimate what they would pay.
In April last year, many deals rose by 7.7%, in line with the Consumer Price Index announced in February as 4%, plus an additional 3.9%. Other deals rose by up to 8.8% in line with the Retail Price Index, which was 4.9%, plus 3.9%.
This also complicated the process of comparing firms when shopping around for a new deal.
Natalie Black, Ofcom's group director for networks and communications, said: "More than ever, households want and need to plan their budgets. Our new rules mean there will be no nasty surprises, and customers will know how much they will be paying and when, through clear labelling."
Uswitch telecoms spokesman Ernest Doku described Ofcom's new rules as a "transparency tax for consumers".
He said: "Many providers have now opted for a blanket flat-rate annual price rise that will be even higher than the inflation-linked approach for the average broadband customer.
"So if you're on a cheaper or average-priced contract, the luxury of knowing what your exact price rise is in advance comes at the cost of an even steeper bill hike: effectively a 'transparency tax' for consumers."
Tom MacInnes, director of policy at Citizens Advice, also said: "It is clear already that there will be customers who will end up seeing bills not only rise above inflation but potentially by more than they would under the previous model."
According to Martin Lewis's Money Saving Expert site, it is possible to end a phone contract during its term, though this may incur a "substantial fee to end it early".
For broadband contracts, an exit fee is also likely unless prices have been raised beyond what was set out in the contract, or the connection quality has been poor. Money Saving Expert also says it is possible to haggle for a better deal mid-contract.
Several providers offer contracts that do not contain price rises, while others offer deals that allow for unspecified price rises during the contract period. If they do this, they must give customers 30 days' notice and the right to exit penalty-free, so consumers can avoid the increase.