Passport applications face disruption due to five weeks’ of strike action from next month.
The action is likely to have a “significant impact” on the delivery of passports as the summer approaches.
More than 1,000 members of the Public and Commercial Services union (PCS) working in Passport Offices in England, Scotland and Wales are to walk out from April 3 to May 5.
The strike will involve those working in Durham, Glasgow, Liverpool, London, Newport, Peterborough and Southport.
Members in the Passport Office in Northern Ireland are being balloted and “may well” join the action subject to the ballot result which closes today (Friday).
The action was described by the union as a “significant escalation” of a long-running dispute over pay, pensions, redundancy terms and job security.
PCS general secretary Mark Serwotka said: “This escalation of our action has come about because, in sharp contrast with other parts of the public sector, ministers have failed to hold any meaningful talks with us, despite two massive strikes and sustained, targeted action lasting six months.
“Their approach is further evidence they’re treating their own workforce worse than anyone else. They’ve had six months to resolve this dispute but for six months have refused to improve their 2% imposed pay rise, and failed to address our members’ other issues of concern.”
The Business Travel Association estimated that more than one million passport applications are due to be processed during the strike period
Chief executive Clive Wratten said: “The Passport Office strikes will have devastating consequences for business travel and the UK economy.
“These strikes will impact businesses across the UK resulting in loss of sales and deals which will cause further damage to the industry and economy which has so far observed a bounce back.
“With over one million applications due to be processed over the strike period we strongly urge the government to come to an agreement with the PCS as soon as possible, to avoid another summer of discontent.”