More than 1,000 construction workers were due to strike at Sellafield nuclear power station this morning.
Trade union Unite said staff from 15 subcontractors working on the decommissioning project at the Cumbrian plant would down tools for two and a half hours from 5.30am.
They are calling for creation of a full-time union convenor role on site to address health and safety concerns and improve welfare facilities.
Unite regional secretary Mick Whitley said: “Workers want to work in a safe environment with constructive industrial relations.
“Our members are sick and tired of being treated like second class citizens on one of Europe’s biggest construction projects. We would urge Sellafield Ltd and the sub-contractors to start treating their workers as partners and enter meaningful talks.”
Sellafield Ltd confirmed a strike took place but said the dispute was between the contractors and their staff and that any delay to work on site was regrettable.
“We urge a speedy resolution in order to ensure the contractors and employees concerned are fully focused on delivering progress at the site,” said a spokesman.
“During any industrial action, our overriding priority is the safety and security of the site and measures are in place to ensure this is maintained during this action.
“This is a dispute about the welfare of workers in the contractor community and not about the safety of the Sellafield site. Sellafield is a safe place to work, as proved by our track record, with 2014/15 producing one of our best ever set of safety statistics and eight gold awards from the Royal Society for the Prevention of Accidents.”
The Cumbria power station, which started generating electricity in the mid-1950s, entered a formal decommissioning phase in 2005.
Well over 1,000 buildings will be decommissioned in an operation expected to take more than 100 years.