The controversial Hinkley Point C nuclear project is set to face further delays after unions representing construction staff announced a ballot on strike action over a pay dispute.
The dispute, which has been ongoing since the spring, concerns the fact that pay rates for civil engineering contracts are less than the rates offered to mechanical and engineering staff.
More than 95% of members polled by the GMB and Unite unions rejected the pay increase offered by EDF – the French utility firm contracted to build the 3,200-megawatt power station in Somerset.
The unions said they would now go ahead with notifying EDF of their intention to ballot members on strike action.
"Members have made their views clear; the unions warned the amount of money being offered was not sufficient and this has proved to be the case," said Jerry Swain, Unite national officer for construction.
"The client and contractors need to understand that this is a high profile, complex project, built in a tightly controlled secure zone, which is being built in an isolated part of the UK.
"It cannot and will not be built on the cheap."
A ballot on strike action at Hinkley Point was called off in June after an interim agreement on bonus payments was agreed.
Unions had hoped to strike a permanent deal on pay for the more than 1,000 civil engineering staff working on the project by September.
Phil Whitehurst, GMB's national officer for construction, said: "The ballot result is a clear indication that the national officers of both GMB and Unite have to get back round the table with EDF as matter of urgency.
"We will be seeking meetings with EDF as soon as possible to solve this situation on behalf of our members."
EDF said it was "disappointed" that its pay offer was rejected by the unions and added that the terms offered were "superior" to norms in the UK construction industry.