A strike by passport workers was "solidly" supported, with the threat of further industrial action unless a row over staff shortages is resolved.
The Public and Commercial Services union said its 2,200 members involved in the dispute mounted picket lines outside Passport Offices across the country during the one-day walkout, and received backing from members of the public.
The union has been warning that staff shortages have led to a huge backlog in processing passport applications this year.
"Although offices have been open, services were massively reduced, so the strike has had an impact," said a union spokesman.
"We have had good support from members of the public, even among those turning up at offices with applications. The ball is now in management's court."
Extra staff were drafted in to deal with a backlog of 30,000 applications earlier this year, and Home Secretary Theresa May issued an apology to those affected by the delays.
The Passport Office said it had fa ced the highest demand for applications in the last 12 years, adding that predictions for the summer surge were " substantially exceeded".
HM Passport Office chief executive Paul Pugh said earlier this month that the 775,000 applications received in June "I think is the highest ever recorded in a single month".
PCS general secretary Mark Serwotka said: "The staffing crisis in the Passport Office has been obvious for everyone to see.
"We are still a long way off getting a commitment from the agency that it will work with us to put the proper resources in place to ensure these backlogs do not reoccur year after year."
The Home Office criticised the union for the timing of the strike, saying it could affect people's summer holidays.
"We are disappointed the PCS leadership has called this strike given that HMPO has been in discussions with the union on their issues of concern," said a spokeswoman.
"Holding a strike at this stage is irresponsible and will only inconvenience our customers and jeopardise their holidays.
"We strongly urge PCS to reconsider this action which is not in the interests of staff or the general public they are dedicated to serving.
"HM Passport Office staff know how important it is to hard-working people and their families to receive their passports in time for their summer holidays. They have shown this through their hard work and commitment during this exceptional period of high demand."