A dispute between mobile operators 3 Ireland and Tesco Mobile means that calls between the networks are not being connected.

It is understood that 3 Ireland believes Tesco Mobile is seeking too high a fee to connect calls from 3 Ireland's subscribers to its network.

Tesco Mobile is a 50/50 joint venture between supermarket giant Tesco and mobile operator O2. It is a virtual operator, meaning it does not have its own network infrastructure but routes its calls over the O2 network. 3 Ireland is thought to be arguing that because Tesco Mobile does not have the cost of maintaining a network, the fees it is seeking are too high.

This week 3 Ireland made an official complaint to the Communications Regulator (ComReg) and asked it to use its dispute resolution procedures to intervene in the row.

A spokesman for ComReg said: "We are very concerned about this because it is impacting customers, and we are in discussions with both sides to try and resolve it as quickly as possible."

A Tesco Mobile spokesman said the company was "working with ComReg to find a way forward".

"It is disappointing that a competitor would deny their customers the opportunity to call their friends, family and colleagues on the Tesco Mobile network."

Last summer Vodafone, O2 and Meteor agreed they would reduce the connection fees they charge other operators to 7.99 cent by the beginning of 2012 from their current level of 10-12 cent.

As the latest entrant to the market the interconnect fees charged by Tesco Mobile are unregulated. ComReg can only dictate a price for fees when an operator is deemed to have significant market power (SMP).

This month ComReg published a draft decision that 3 Ireland has SMP for connecting calls to its own network. 3 Ireland can appeal this decision, which would enable ComReg to dictate its interconnect fees, before February 12th.

3 Ireland declined to comment, citing commercial discussions.