O2 is increasing its home broadband prices by almost £50 per year in some cases, according to price comparison site Moneysavingexpert.com.
The rises will hit new and current customers. They received the notice this week.
According to Ofcom rules, most broadband contracts allow providers to increase costs with 30 days warning without breaching the contract.
Those who signed up to a package from September 2010 will see an increase of between 33p and 58p per month.
Meanwhile, those on older O2 packages will see steeper price increases of between £1.84 and £3.63 per month.
Customers on O2's Access package, which enables them to connect via a BT landline, will face hikes of between £2.63 (pre-September 2010) and £4.12 per month (post-September 2010).
Virgin Media will raise costs on one of its seven available packages (the L 10Mb deal) by 75p per month in April.
However, BT, O2, Orange, Sky and Talk Talk told Moneysavingexpert that they have no current plans to raise broadband prices.
An O2 spokeswoman said: ‘We want our customers to continue to receive a great service, which means investing more in our network and, as a result, we are increasing our prices.’