People with mobile phones on the EE network are facing a jump in their bills from the end of March.
The operator has started contacting customers, saying their price plans will increase in line with inflation plus 3.9 per cent.
With January's Consumer Price Index, upon which the rise is being based, set at 5.5 per cent, users are being landed with a total 9.4 per cent rise.
In the message sent to customers, EE said: "For example, a £25.00 price plan will increase by £2.31 a month.
"Your out-of-bundle charges and other add-ons will also increase in line with the CPI rate of inflation plus 3.9 per cent.
"For example, a £1 add-on will go up by £0.09 a month. Calls and texts to EU countries from the UK will also increase on the same basis and will increase as of 31 March each year by the CPI rate of inflation published in January plus 3.9 per cent.
"This change will take place 30 days after you've received this text."
Customers were directed to the EE website to find out more about the changes.
EE also said it would be updating customers' terms with effect from June 1, based on changes to Ofcom rules.
More details can be found at http://discover.ee.co.uk/d4G101e3.
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