About 80 permanent site workers are involved, plus a similar number of agency workers. They are members of the GMB and Unite unions. The site is not covered by the Naeci agreement.
GMB local official Brian Negus said: "It has come down to a trial of strength. The process of working out a pay deal took seven months. There wasn't a bad offer from the employers. It was worth 6.25% and I felt able to recommend it.
"But the men voted overwhelmingly against it. They are adamant that they want what they perceive to be the union rate. They are doing Naeci work. And that is the rate they want. I want to see my members back at work, but there is no movement. There has been a conciliation approach from ACAS. However, the workers are just not interested."
Burntisland Fabrications declined to comment.