A planned strike at the Sellafield nuclear processing plant in Cumbria is back on after union officials said talks between management and the union broke down.
Both sides say safety has not been affected during the strikes
But British Nuclear Fuels (BNFL) has said as far as it was concerned negotiations were continuing.
The GMB union had been in talks with British Nuclear Fuels (BNFL) at the conciliation service Acas on Wednesday to try to avert further walkouts.
Unions have accused BNFL of reneging on an agreement to close a £2,000-a-year pay gap between manual and white collar staff.
About 350 workers have held three walkouts in a dispute over shift pay.
A further strike by workers at the site had been planned for Friday but was suspended because of the fresh talks.
But the GMB said the talks had broken down and the strike would now go ahead.
A union spokeswoman said: "We are really disappointed. We were going to suspend our strike action as a sign of good faith but the company has refused to negotiate with us.
"We remain committed to resolving this dispute and negotiating with the
company but BNFL has to play its part as well."
Workers at Sellafield have already taken industrial action over the pay row.