Workers at the Passport Office may go on strike over the growing backlog, as warnings emerged that hundreds of thousands of Brits could miss their summer holidays due to delays.
Up to 500,000 people may not get their passports before their planned departure date, as the department struggles to get on top of the backlog.
Hundreds of constituents have complained to their MPs about the service, as they consider having to shell out £55.50 extra for the fast-track service which would guarantee they get their passport back in time.
The Passport Office blamed the surge on "the improving economy and a rise in holiday bookings", saying it has received 300,000 more applications since January than in the same period last year.
But the Public and Commercial Services union (PCS) has written to Passport Office chief executive Paul Pugh blaming the delays on "major job cuts and office closures during the past five years", as well as the increased use of private companies.
The letter states that 22 interview offices and one application processing centre have closed in recent years, with 315 staff – a tenth of the workforce – losing their jobs.
"We do not accept that the current problems can solely be down to unusual demand," the letter states.
The union is preparing a consultative ballot of its 250,000 members with a view to taking joint action over pay, probably starting with a one-day strike in July.
PCS is demanding negotiations on additional permanent jobs, action on low pay and talks on future privatisations.
"If we do not get a satisfactory response by June 30th 2014 we will be considering industrial action," it reads.
A quarter of staff employed who track fraudulent paperwork have now been transferred to help out with delayed applications, leading to warnings about the integrity of the system.
PCS general secretary Mark Serwotka said: "The passport office is failing holidaymakers because of a political decision to cut staff and close local offices.
"While the economy is showing signs of recovery for some, the damage being done by the government's spending cuts is evident to anyone trying to get a passport at the moment and we are not prepared to stand by and allow this to happen."