Sky currently charges ITV £17m a year for access to its EPG service. Under a new deal, Sky is proposing that ITV pay between £13m and £17m to ensure viewers in different areas pick up the correct news and programming dedicated to their ITV region.
ITV is insisting that Sky is overcharging the network and the fee should be more like the £4m rate the BBC pays.
In a statement, ITV said that the charges are neither fair nor reasonable. "The charge proposed by Sky for the service is not fair and reasonable and it is discriminatory when compared to charges made to other broadcasters for related services."
Sky is defending its charges and will argue the case for them to the media regulator.
A Sky spokesman said: "We look forward to demonstrating to Ofcom that the charges we propose for ITV are consistent with our regulatory obligations."
ITV, which needs to air on the Sky platform to maximise ad revenue and ratings, is hoping that the investigation will force Sky to come up with a better offer.
The investigation will take until early May to complete and is the first time that the regulator has had to settle a dispute between two broadcasters.
In 2003, there was a similar row between Sky and the BBC, which ended after the satellite network backed down and agreed to cut its proposed charges.
Last November, when ITV's new drama channel for the 35-plus market ITV3 was launched, it was only made available on Sky after a last-minute deal that saw the network buy Sky Ventures' 49.5% stake in its multichannel operation, Granada Sky Broadcasting.
It was originally only intended for Freeview and cable launch after negotiations between the Sky and ITV broke down.
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