Hitachi suspended work on the new Wylfa Nuclear Power Plant in northern Wales in a move that marked a "huge blow" to the British economy.
The 20 billion pound planet from Anglesey would have had to hire 9,000 people during construction, working on two nuclear reactors.
Hitachi's British group, Horizon, has failed to find private investors for this plant – which has promised to provide about 6% of UK electricity.
Union leaders have marked "devastating" development, and the government has fired because it did not support the plan.
Last week, Prime Minister Theresa May said he talked about Wylfa Newydd with Japanese Prime Minister Shinzo Abe – but said any decision would be "commercial" by Hitachi.
The company said, despite talks with the British and Japanese governments, that it failed to reach an agreement in favor of all parties.
In an announcement announced this morning by Horizon – Hitachi in the UK, the company said it would freeze plans for a new nuclear project in Wales.
"Consequently, we will suspend the development of the Wylfa Newydd project, as well as Oldbury's work, until a solution is found.
"Meanwhile, we will take steps to reduce our presence, but we will retain the option of resuming future development," Horizon CEO Duncan Hawthorne said in a statement.
The company suggested that rising construction costs could force the move.
The Anglesey Council said that if the project had stopped, it would be a "huge blow" for the economy in northern Wales.
Welsh Economy Minister Ken Skates told the BBC in advance: "If it's interrupted, work should start immediately between governments and local government and the business community to ensure there are short-term employment opportunities while we find a new investor for the project. "
And Secretary of the Galle Alun Cairns said it would be "the largest infrastructure project in Wales for a generation."
Research has suggested that they will bring 7.7 billion pounds to the Welsh economy.