Hundreds of workers at the Driving and Vehicle Licensing Authority (DVLA) are to stage fresh strikes in a long-running dispute over Covid-related safety.
Members of the Public and Commercial Services (PCS) union based in Swansea, South Wales, will walk out from Tuesday to Thursday.
The Swansea offices are responsible for vehicle tax across the UK.
A series of strikes has already been held and the union is warning of months of industrial action unless the row is resolved.
The union is calling for a reduction in the number of staff expected to work from the office.
The DVLA says it has taken measures to ensure the safety of workers and has followed official guidance.
PCS general secretary Mark Serwotka said the DVLA and Department for Transport were not interested in settling this dispute.
He accused managers of hiring contractors to carry out the work of those on strike.
"The cost of using a contractor to carry out work done by DVLA staff could be used to settle the dispute alongside putting the original deal back on the table," he said.
"Instead, public money is being wasted on trying to undermine our legitimate strike action, which will only have the opposite effect.
"Targeted action will continue at the DVLA for months to come unless the original deal, which both parties had agreed in principle, is back on the table,"
A DVLA spokesman said it will be temporarily use an external supplier to print and despatch some of its post, due to the strike.
"This will ensure that during this temporary disruption we can continue to print and mail essential documents such as driving licences, vehicle documents and vaccine letters which we manage on behalf of several NHS trusts," he said.
"With PCS choosing to continue with industrial action and targeting services that will have the greatest negative impact on the public, we must, where we can, continue to find ways to deliver our services for our customers - we cannot simply stop printing and posting essential documents at this time."
