Interconnector cables are required to allow Scotland's islands to export extra energy to the mainland that will be generated from wind, wave and tidal projects in future. Their current infrastructure is at full capacity.
The Western Isles had been due to have a new connection to Lewis in place by 2015 but now that will be 2016 at the earliest, while Orkney and Shetland had been due to be connected by 2016 but now it will be 2018 at the earliest.
Western Isles Council leader Angus Campbell is warning that unless a contract can be signed to place an order by June for a new subsea cable, it would put everything back three years.
"It would mean we would miss the boat, and Scotland would lose the best sources of renewable energy in the land," he said.
He was speaking after news that Scottish Hydro Electric Transmission, a subsidiary of SSE, held talks with the UK and Scottish governments on the rising cost of a subsea cable to transmit green energy from the islands to the mainland. Last month SSE said the cost of laying the cable to the Western Isles had risen 65% to £775m.
Ministers are understood to be deeply concerned slippage and increasing costs are jeopardising their keystone policy of green energy development on the islands. A spokeswoman said: "The Scottish Government is disappointed by this delay and will discuss with SSE as a matter of urgency."