Trade Union GMB says the UK has an increased risk of power shortages due to over-dependence on unpredictable renewables and an unchanging demand.
Providing support for the delayed Hinkley Point nuclear power station, trade unions GMB, Unite, Ucatt, and Prospect have stated that confirming financial go-ahead for the project will be the first big test for infrastructure projects following the Brexit vote.
These four trade unions addressed a letter to EDF Energy's chief executive Vincent de Rivaz, which will make the final investment decision (FID) for the Somerset plant.
The letter read: "The UK trade unions are 100% in support of Hinkley Point C and believe it vital to make a final investment decision in a timely fashion after the consultation process (between EDF and the French unions) is completed.
"Nuclear new build is already behind the curve and we cannot afford further delay. It is vital for EDF to make a final investment decision now."
The unions consider the £18bn project to be crucial in terms of providing thousands of jobs and to maintain power supply. The project would generate 7% of UK electricity demand, however the start date for generation has been pushed to 2025 due to delays.
The letter continues: "From an energy perspective, the UK needs the electricity. We are rapidly losing capacity and this process will continue as the UK coal and nuclear stations reach the end of their operating lives.
"At the same time, we are committed to transitioning to a carbon-neutral balanced energy policy in the UK, including nuclear and renewables.
"Much is at stake in both France and the UK in terms of jobs, skills, social dialogue, industrial capability, and prosperity into the future."
The letter also added: "It would be a tragedy, in both France and the UK if all this work and the extraordinary opportunities it provides were to be lost.
"The moment to make the decision is upon us and we have a genuine fear any further delay will lead to the unravelling of all that we have fought so hard achieve."
Ucatt's general secretary Brian Rye said: "This is a vitally needed and ground-breaking project. The decision on the final go-ahead on Hinkley will demonstrate whether foreign-owned companies are still prepared to invest in the UK. The government needs to ensure that they get this deal over the line."