Staff at West Burton B gas-fired power station have opted for Prospect to negotiate their pay and conditions.
When the station opened in 2012, all staff were placed on personal contracts.
Following a long campaign led by Prospect, with the support of GMB and Unite, the staff at the power station voted overwhelmingly in a ballot for Prospect and the other unions to represent them in consultations and negotiations.
Prospect negotiator Mike Macdonald said: "With more than 90% of staff choosing union representation, this is a substantial vote of confidence in our ability to represent staff in modern workplaces.
"We look forward to working with EdF Energy to develop pay structures and a process for change that will enable our members to adapt to a rapidly changing energy market."