The British Passport Office workers have gone on a five-week strike.
This followed dispute over jobs, pay, pensions and conditions.
Over 1,000 members of the Public and Commercial Services union (PCS) at eight sites walked out, according to general secretary, Mark Serwotka.
Serwotka said picket lines will be mounted outside the offices in Glasgow, Durham, Liverpool, Southport, Peterborough, London, Belfast and Newport in Wales.
The official accused ministers of treating its employees differently to others in the public sector despite talks with health workers and teachers.
The union has assured that those protesting will be supported by a fund. A letter has been sent to the government calling for negotiation.
A demonstration across the country is expected to be attended by more than 130,000 civil servants on April 28.
The Home Office had announced that the passport office already processed more than 2.7 million applications this year.
