Ofgem announced plans in August to cut the charges per unit of electricity for firms generating power in the north of Scotland. Charges for putting power into the grid in that area are currently high and have been seen as a barrier to renewable energy investment.
But now that change in transmission charges has been put off for a year.
The decision prompted Enterprise and Energy Minister Fergus Ewing to express "extreme disappointment" at Ofgem's announcement of a further year's delay in introducing measures to the tackle the long term formula on Scottish electricity generators.
He said: "After three years of exhaustive examination of electricity transmission charging and associated connection arrangements, Scottish generators are facing a further three months of uncertainty - and further 12 months before any new arrangements take effect - while the benefits for consumers risk being delayed."
Tom Greatrex, Scottish Labour's Shadow Energy Minister and MP for Rutherglen and Hamilton West, commenting on Ofgem's delay to Project TransmiT, said: "Project TransmiT uses an evidence-based approach to ensure that the costs of transmission are fairly distributed and it is frustrating that these reforms will now be one year late.
"The SNP's plan of a postage-stamp model for transmission costs would leave the consumer with an additional £7bn bill.
The SNP's own plans for distributing transmission costs are an expensive fantasy that ."
Niall Stuart, chief executive of Scottish Renewables, expressed concern: "After three years of analysis and consultation, Ofgem had proposed a series of changes which would have lessened the gulf between the high electricity transmission charges in the north of Scotland and the charges in southern parts of the UK.
"This announcement now means that generators in Scotland will not see any reduction in their charges next year, and generators in the south of the UK will continue to pay significantly less, or even receive a subsidy, for connecting to the grid - a system which is totally out of step with the need to change the way we produce electricity in order to cut carbon emissions."
Patrick Harvie of the Scottish Greens said he was worried by the decision.