Workers at dozens of Driving and Vehicle Licensing Agency (DVLA) offices are staging a 24-hour strike in a dispute over closures and job losses.
Members of the Public and Commercial Services union (PCS) at 39 local and 10 enforcement offices in England, Scotland and Wales will take part in the industrial action.
The union is campaigning against planned office closures across the country, arguing it signals the end of a "highly prized" face-to-face service to motorists.
The union has delivered a 72,000 name petition opposing the closures, to the Department for Transport, saying it was the largest paper petition it had ever organised.
A union spokesman said: "Our petition was signed by members of the public, motor traders, representatives of motor trade federations and haulage and bus companies, and representatives of historic vehicle clubs.
"We're very concerned about the lack of awareness among people that the offices are set to close or even that a consultation has been carried out."
PCS general secretary Mark Serwotka said: "As well as losing a high quality public service and more than 1,000 jobs at a time of high unemployment, we believe these closures will lead to increased vehicle tax evasion and fraud. We want the minister to listen to the overwhelming views of the public, motor traders and his staff, and to see sense and reverse these ill-thought through and damaging closures."
DVLA said it could not guarantee a business-as-usual service because of the strike and asked people to avoid travelling to any DVLA office today.
Contact centres will be operating a reduced service and callers were warned to expect longer waiting times.
The organisation suggested conducting transactions by other means such as electronically or via the Post Office.