Permanent jobs need to be "put back" into the passport office if another backlog is to be prevented, according to the union which represents their workers.
Mike Jones, from the PCS union, said passport office employees were walking out because there needed to be "a permanent solution" to the staffing shortages which had caused the original backlog.
More top news
Inflation fell from 3.1% in November, to 3% in the last month of 2017.
Wintry scenes with rain, sleet & snow
Residents have been ordered to evacuate around Mount Mayon in the Philippines as lava and ash flows from its tip.