Unite has called for B&ES to increase its pay offer after workers voted nine to one to reject the deal.
Skilled plumbers, and heating and ventilating engineers, voted nine to one against accepting a two-year pay offer which included freezing pay for the first year, followed by 1.5% increase for the second year.
Unite said the country's low carbon energy sector could be affected if industrial action follows a breakdown in talks as thousands of skilled workers down tools.
Bernard McAulay, Unite national officer for construction, said: “This pay offer has been roundly rejected by our members. The employers are hiding behind the economic climate. We know that the major contractors that make up the Building & Engineering Association have healthy profit margins and order books. Last year they attempted to de-skill the industry causing the biggest industrial unrest on sites across the country for a decade.
“After six months the employers had to back-track because of the opposition they felt by thousands of angry skilled workers. This pay deal has been received with equal anger and Unite members have made it clear that they want an improved offer."
If the Association refuses to improve its offer, Unite has said it will consider moving towards an industrial action ballot, claiming that potential industrial action by skilled workers could jeopardise the government's ability to meet its low carbon energy targets.