Steria UK IT support and admin staff working for the UK's Identify and Passport Service have voted to strike over a low pay offer.
The workers, who are members of the Public and Commercial Services (PCS) union, plan to walk out for two days at the end of July. They have threatened further action next month if necessary.
The industrial action would cause significant delays for people applying for or renewing passports, the union claimed.
The employees have previously rejected an imposed pay freeze for staff earning £21,000 a year and above. For those earning less, Steria is understood to have offered a pay rise below the level of inflation that is equal to an average of around £180 pro-rata over a nine-month period.
More than 160 workers on the passport offices contract are paid just £13,500 a year, according to PCS.
"These private sector staff provide an invaluable public service for UK citizens applying for or renewing their passports.
"Yet instead of rewarding its workforce with a decent pay rise, the company is imposing what is nothing more than a pay cut at the same time as pocketing millions in profits," said Mark Serwotka, PCS general secretary.
Steria made a group pre-tax profit of 70.9 million (£63 million) in 2010, and PCS claims that the company's six top executives, including John Torrie, its UK CEO, earned 2.5 million between them.
The company had not provided a comment at the time of writing.