IT staff at HM Revenue & Customs are among 70,000 union members being balloted for strike action over planned job cuts.
The ballot is being held by the PCS union from today, with a "yes" vote in the ballot leading to a one-day strike on 31 January - the deadline for self-assessment tax returns.
This action would then be followed by an overtime ban at an organisation which has recently shed 13,000 jobs.
The PCS said previous job losses had contributed to several recent data breaches at HMRC, not least the threat to personal details of 25 million people when data disks went missing last year.
With 13,000 jobs gone and a further 12,500 planned to go by 2011, the union warned that the department was "in danger of serious service failure".
PCS general secretary Mark Serwotka said, "With office closures and 13,000 job cuts to date, the department is already running on empty, resulting in deteriorating services.
"HMRC cannot deliver a quality service in the face of continued arbitrary cuts and the government and the department need to recognise that HMRC needs to be properly resourced and staffed if public confidence is to be restored."