The British Passport Office workers has commenced a five-week strike amid the 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.