EDF and SSE have appealed against Ofgem’s decision to reject a code modification on charges to generators for the electricity transmission system in 2015/16.
The energy firms said electricity generators were overcharged for using the national transmission system that period and allege it is “unlawful”.
Generators’ network charges in 2015/16 exceeded the €2.50 (£2.23)/MWh cap on transmission charged paid by them, which is set under EU regulations.
Last month, Ofgem however rejected the request to modify the rules that would result in generators receiving a £120 million rebate funded by consumers.
It was on the grounds that most, if not all, local network charges, which mainly relate to transmission links connecting offshore wind farms to the grid, should be excluded from this cap.
EDF said: “We are jointly appealing with SSE against Ofgem’s decision not to refund these extra charges.”
It added if Ofgem’s decision is not reversed, it “risks creating uncertainty in the electricity market”.
The Competition and Markets Authority (CMA) has appointed a group of panel members to decide on permission to appeal by 20th December 2017.
Ofgem said in response: “Electricity consumers will be disappointed to learn that SSE and EDF have chosen to appeal our decision to reject proposals for a rebate of network charges that is likely to cost consumers up to £120 million and lead to increasing payments to larger generators in the longer term.
“Ofgem’s decision is a sensible interpretation of European Union regulations and is in the interests of consumers. We will robustly defend our decision at the Competition and Markets Authority.”