The British passport office workers began a five-week strike in the increasingly bitter civil service dispute over jobs, pay, pensions and conditions.
In an escalation of the protracted dispute, more than 1,000 Public and Commercial Services union members left eight locations, according to PCS General Secretary Mark Serwotka on Monday.
Picket lines will be set up in front of the offices in Glasgow, Durham, Liverpool, Southport, Peterborough, London, Belfast, and Newport, Wales, according to Serwotka.
A strike fund will support individuals participating, according to the union.
Serwotka had written to the administration requesting immediate negotiations in an effort to settle the conflict.
After talks with the unions that represent teachers and health workers were held, he accused ministers of treating their own staff differently from other members of the public sector.
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.