Problems with backlogs and delayed passports are still ongoing after the the highest demand for 12 years.
Yesterday, the PCS walked out over staff shortages saying poor staffing levels were partly responsible for the delays earlier in the year.
Last month the Home Office redeployed hundreds of staff to deal with a backlog of 30,000 applications, but some people are still experiencing delays putting holidays and trips abroad in jeopardy.
14-year-old Megan Richards from Newport is one of thousands of people affected by yesterday's strike.
Megan's grandmother Christine Richards said they had to travel to Peterborough.
"This is the first appointment we could get. We couldn't get one in Newport at all. The people have a right to strike... but when it impacts on you personally it's sometimes a little bit difficult to be sympathetic."
A spokesperson for the Home Office said the strike was 'irresponsible' and will lead to further inconvenience for customers.