Passport Office staff in Durham have been taking part in a national strike today (July 28).
The Public and Commercial Services Union says the one-day stoppage is to draw attention to staff shortages, and inequalities in pay.
The Durham office is open, but only to those who have pre-booked appointments.
The strike comes just weeks after extra staff were drafted in to deal with a massive backlog in applications which have jeopardised the holidays of many.
Management say the service has faced the highest demand for passports in the last 12 years.
The Passport Office is to put more staff and resources in place to deal with a backlog of applications, Home Secretary Theresa May has said.
The government owes apologies to "tens of thousands" of families who face having their summer holidays ruined by delays at the passport office, an MP has claimed.
Geoffrey Robinson, Labour MP for Coventry North West said delays at the Passport Office now ran to 500,000 applications.
"Call them delays, call them in process, call them whatever you want... people in their constituencies are not getting their passports in anything like [the normal time].
"The Government has left it so late in its reaction to this burgeoning problem there is probably no time left to deal with it in the relatively short period we have building up to the holidays - that's one of the tragedies of the situation.
The Home Office says passport office staff are working "seven days a week" to deal with an increase in passport applications amid complaints of delays.
Home Office Minister James Brokenshire said the passport office had taken on additional staff earlier this year to deal with "unprecedented" demand.
He said: "Between January 1 and May 31 HMPO has received 3.3 million applications - 350,000 more than the same period last year, and the highest volume of applications received for this period over 12 years."
"As a result they have put in place a system of measures to deal with it and to see that people receive their passports in good time [...] customer service staff are working seven days a week to process the high numbers of applications."
Some British holidaymakers could have their summer holidays ruined due to lengthy delays caused by an application backlog at the passport office, the Sun (£) has reported.
Passport fraud staff have been diverted to help with the extra workload amid a struggle to issue travel documents before the summer holiday season, the Guardian said.
The Passport Office's interim chief executive Paul Pugh denied there was a backlog, saying: "We have been experiencing exceptional early summer demand for passports. We have brought in extra staff to respond to the extra demand."
Teenagers have been tampering with their own passports in a desperate bid to get served alcohol in clubs and bars.
Northumbria Police have said they have now seized a number of passports and driving licences as they crackdown on the trend in Tyne and Wear.
Officers have warned that anyone found with forged documents faces arrest and prosecution.
Bar, club and shop owners say they have been shown documents in recent months that have had dates of birth obviously changed. All altered documents and passports seized by police will now be cut up and sent to the Passport Office or relevant agencies to be destroyed.