Thousands of staff at the Home Office, including airport immigration workers, have voted to go on strike over jobs, pay and other issues, raising the threat of industrial action hitting the Olympics.
The Public and Commercial Services union (PCS) said 57% of its members had backed a campaign of action in protest at cuts.
Union leaders will meet tomorrow to decide their next move, which could include a walkout at border controls at ports and airports including Heathrow as well as other forms of industrial action such as a ban on overtime.
The union could also decide on new tactics including targeting departments such as the Criminal Records Bureau or Passport Office.
Any strike just before the opening ceremony of the Olympics on July 27 could have a big impact on people travelling to the UK to watch the event, the union believes.
Officials said a work-to-rule and overtime ban could have a big impact on border controls and in passport offices.
The PCS is in dispute with the Home Office on several issues, including plans to cut 8,500 jobs, the threat of compulsory redundancies in the passport office in Newport, South Wales, a 1% pay rise cap following a two-year wage freeze, privatisation of services, and alleged victimisation of union reps.
PCS general secretary Mark Serwotka said the issues which have caused the dispute were flaring in other Government departments, which could also lead to industrial action.
Mr Serwotka said: "Ministers have known about these issues for a very long time but have chosen not to act.
"We believe they have acted recklessly and irresponsibly in cutting so many jobs and, in the case of the UK Border Agency, they have simply tried to paper over the cracks by deploying severely undertrained staff at our borders.
"If these issues are not resolved, they threaten to seriously undermine the Home Office's ability to provide vital public services, and we cannot sit back and allow that to happen."
The union said cuts in the Border Agency was causing "chaos" and leading to long queues at airports such as Heathrow.
PCS members at the Department for Transport, including driving test examiners and Coastguards, have been taking industrial action over the past few weeks, while staff in other Government departments including the Ministries of Defence and Justice, are set to vote in the coming weeks on how to campaign against cuts.
Around 16,000 PCS members in the Home Office were balloted, with a 57% vote for strikes and 75% majority for other forms of action, on a turnout of 20%.