The Department for Transport says its "disappointed" that 4,000 members of staff have decided to strike today.
The PCS union says members will hold 15 minute demonstrations across Wales.
We are disappointed that the PCS union have decided to take industrial action while we are still engaged in consultation with them about their concerns over changes within the department.
Contingency plans are in place to ensure delivery of essential services to the public continues throughout the planned strike action.
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Showers expected throughout the day especially in the north. Drier and brighter elsewhere but cooler than in recent days.
Most places will become dry overnight, although it will remain generally cloudy with patches of hill fog.
Police have told people in Pontypridd that the cordon around the rugby club could be in place until next week.