British Passport Office workers began a five-week strike in the increasingly bitter civil service dispute over jobs, pay, pensions and conditions.
More than 1,000 members of the Public and Commercial Services union (PCS) at eight sites walked out in an escalation of the long-running row.
PCS General Secretary, Mark Serwotka, said on Monday
According to Serwotka, picket lines will be mounted outside the offices in Glasgow, Durham, Liverpool, Southport, Peterborough, London, Belfast and Newport in Wales.
The union said those taking action will be supported by a strike fund.
Serwotka had written to the government, calling for urgent talks in a bid to resolve the dispute.
He had accused ministers of treating its own employees differently to others in the public sector after negotiations were held with unions representing health workers and teachers.
The union is stepping up strikes, with a nationwide walkout of more than 130,000 civil servants planned for April 28.
The Home Office said the passport office had already processed more than 2.7 million applications this year.
It added that over 99.7 per cent of standard applications were being processed within 10 weeks, with the majority of those delivered to customers well under this timescale.
However, there are currently no plans to change official guidance which states that it takes up to 10 weeks to get a passport.
