Workers at the Sellafield nuclear reprocessing plant are increasing their strike action.
Members of the GMB and Amicus will walk out today over two shifts, halting operations at BNFL's Cumbrian plant.
The unions claim that BNFL has reneged on an agreement to close a £2,000 sterling pay gap between white collar staff and manual workers. The company denies the charge.
The unions said an agreement had been made to harmonise pay by next April, but the company was now insisting the process could not be completed until 2009.
A single shift strike was held last week and further walkouts are planned, although safety cover is being provided.
Mr Brian Strutton, national officer for the GMB, said: "We had hoped that last week's action would have convinced BNFL to meet with us but our calls for meetings have still been met with refusal. We have no choice but to escalate the action until BNFL agrees to talks.
Strikes are set to continue every Friday until December 12th if the dispute remains unresolved.