Plans for a £20bn nuclear power plant on Anglesey that would have created thousands of jobs are set to be scrapped.
The leader of Anglesey Council, Cllr Llinos Medi, said she had been informed that the Japanese company Hitachi "intends to withdraw" from the project.
Cllr Medi described the news as a "devastating blow" and said she would be calling for an urgent meeting with both the UK and Welsh Governments.
She said: “If this decision is confirmed - then it will be a devastating blow to the Anglesey economy. The Wylfa Newydd project had the potential to transform the Anglesey and North Wales economy, particularly that of North Anglesey.
“I will be calling for an urgent meeting with both UK and Welsh Governments to discuss the future of the Wylfa site.”
The tech giant is expected to announce on Wednesday that it has scrapped plans for the multi-billion pound power station in North Wales, but the project developer Horizon Nuclear, which is owned by Hitachi, said it would not comment.
Hitachi announced it was suspending its involvement in the Wylfa Newydd project in January 2019 after failing to reach a funding agreement with the UK Government.
Justin Bowden, national officer of the GMB union, said: "This utterly predictable announcement from Hitachi is the outcome of successive government failures to act decisively around new nuclear, and in particular how it is financed.
"New nuclear is vital in achieving decarbonisation, especially when teamed up with hydrogen.
"It's no coincidence that around the world - almost without exception - it's governments who finance these projects, as they are the lender of last resort when it comes to keeping the lights on.
A group of 100 organisations, including unions and businesses, backing plans to build a nuclear power station at Sizewell in Suffolk, voiced concern about the Wylfa decision.
A spokesperson for Nuclear Free Local Authorities (NFLA) said it understands via Japanese media reports that Hitachi will announce its plans to withdraw from the project at a board meeting on Wednesday.
NFLA Welsh Forum Chair, Councillor Ernie Galsworthy, said: “I am not surprised at all to hear that Hitachi is likely to call a final halt to its 8 year interest in developing new nuclear at Wylfa in its board meeting tomorrow.
"The writing has been on the board for some considerable time, and it is clear recent negotiations with the UK Government have failed to satisfy the Japanese company that it could move forward with this project.
"This should now mean the end of interest in new nuclear in Wales and start the process of moving away from these costly projects towards renewable energy alternatives, energy efficiency and energy storage schemes in which Councils can play a positive role in."
There are warnings that the country faces a potential energy gap during peak winter times and Stephen Crabb, chairman of the Welsh Affairs Committee, said the decision was a "blow" for Wales.
"The decision of Hitachi to pull out of the Wylfa nuclear project is a blow for Wales and the UK's ambition to achieve net-zero carbon emissions by 2050.
"This was set to be the largest energy project Wales had ever seen with a positive impact on skills and employment in the region.
"Reassurances were made of Hitachi's commitment to the project over the summer that gave hope to the workers who'd be needed to construct it and the high-skilled employees who would run it.
"With the nation's remaining nuclear plants ageing and the need for low-carbon, high-yield plants needed to replace them urgent, it has never been more important than now to ensure energy security."