Hundreds of workers at the Driver and Vehicle Licensing Agency have launched fresh industrial action in a long-running dispute over Covid-related safety.
Members of the Public and Commercial Services union at the DVLA site in Swansea went on strike on Wednesday until Saturday.
The union warned it was entering a new phase of “sustained and targeted” industrial unrest for months to come.
The latest strike is the third time staff have walked out over demands for more safety measures.
The DVLA insists it has done everything possible to keep workers safe and has followed official guidelines.
PCS general secretary Mark Serwotka said a deal was all but agreed to end the dispute, claiming it was suddenly withdrawn at the 11th hour without any explanation.
He said: “Through painstaking negotiation, our union and DVLA senior management were on the verge of agreeing a deal only for it to be scuppered at the last minute.
“We strongly suspect senior ministers at the Department for Transport have interfered with the progress we were making and want to make some kind of ideological stand against PCS.
“They have grossly underestimated the resolve of our members in DVLA and have only emboldened them to take targeted and sustained action in the months ahead until they win.
“PCS is fully prepared for months of strike action, and we urge the Government to rethink its position.”
A DVLA spokesman said: “It’s disappointing to see the Public and Commercial Services Union not only choose to continue with industrial action when there are zero Covid cases at DVLA, but they are also specifically targeting areas of the organisation that will have the greatest negative impact on the public, including some of the more vulnerable people in society, just as restrictions are starting to ease.
“The DVLA has worked closely with Public Health Wales along with Swansea Environmental Health and the Health and Safety Executive who have conducted regular site visits and inspections and have repeatedly confirmed a high level of compliance with control measures.
“Millions of people right across the UK are relying on essential DVLA services and PCS’s demands will cause significant and unnecessary disruption to families and businesses, all at a time when they are most needed.”