Workers at the British Passport Office started a five-week strike as the civil service dispute over employment, pay, pensions, and conditions grew more acrimonious.
In a worsening of the protracted dispute, more than 1,000 Public and Commercial Services union (PCS) workers left eight locations.
Mark Serwotka, the general secretary of the PCS, said on Monday Picket lines will be set up in front of the buildings in Glasgow, Durham, Liverpool, Southport, Peterborough, London, Belfast, and Newport, Wales, according to Serwotka.
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.
Open Letter
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.
