Swisscom could be forced to hand partial refunds to rivals on fees paid to access its fixed network, after regulator Federal Communications Commission (ComCom) retrospectively reduced regulated prices for 2013 to 2016.

ComCom reviewed rates charged by Swisscom for use of its copper network following complaints from rivals Salt and Sunrise. It used a new cost model, which takes into account the increased use and deployment of fibre across the country.

Its preliminary report concluded access fees should have been lower for leased lines, network interconnection and last mile connectivity. Other aspects of its wholesale rate were unchanged.

Reductions vary from a 10 per cent cut for access to some unbundled copper lines, to 80 per cent lower charges for some leased lines.

In a statement, Swisscom said the leased line cuts of between 65 per cent and 80 per cent were “difficult to comprehend” as the “reductions have arisen from differing assumptions and calculation models within the complex pricing structure”.

This was the only part of the decision it took issue with.

The operator said it will an analyse the decision in detail and consider an appeal to the Federal Administrative Court. It has already made provisions in its balance sheet to cover the cost of the price reductions should they be upheld.

Swiss daily newspaper Blick estimated the cost of ComCom’s decision could run into tens of millions of Swiss Francs.