Freeserve has slammed Oftel for allowing BT to "establish a monopoly" in the broadband market.
The ISP is angry about a recent statement from Oftel concerning BT's forthcoming "no frills" broadband service.
Industry watchdog Oftel has allowed BT to charge customers and market the service via the traditional blue telephone bill.
In a statement Freeserve said that Oftel had gifted BT the anti-competitive advantage of using its blue bill to charge for its own broadband service.
"The blue bill, which supports BT's near-monopoly fixed-line phone business, is a privilege of BT and BT alone. This is a clear example of BT being allowed by the regulator to leverage a dominant market position to establish a position in broadband," said Freeserve.
But Oftel has said there is already plenty of competition in the broadband market.
"Just because the information is available on one bill doesn't necessarily mean that people will choose it," said a spokesperson for the regulator.
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