A row over bonus pay is threatening to lead to an industrial dispute among construction workers at the site of the new Hinkley Point power station.
A consultative ballot is to be held among 700 members of the Unite and GMB unions, which could lead to a vote on industrial action.
The unions claim contractors at the £18 billion project in Somerset have failed to pay a predicted bonus.
Union official Rob Miguel said: “The Hinkley Point nuclear power station is key to the future energy needs of the UK.
“The project has already suffered delays and to achieve the 2025 start date for electricity generation, a skilled construction workforce is required.