Home Office ministers are urgently considering taking court action over Thursday's planned 24-hour strike by Heathrow immigration and customs staff on the eve of the Olympics.
The possibility of an injunction to block the industrial action by the Public and Commercial Services (PCS) follows a letter to the union by the home secretary, Theresa May, describing the planned walkout as "opportunist and wholly unjustified".
PCS officials are due to hold talks with senior Home Office management later on Tuesday.
Home Office minister Lord Henley told the House of Lords: "We are currently checking the legality of the strike and, if satisfied it is illegal, we will take the appropriate remedies in the courts."
He claimed that on the previous four occasions that the PCS had staged 24-hour strikes at Heathrow contingency measures had meant that border security had been maintained without triggering excessive queues. Henley added that only 12% of the union's Home Office membership had voted to take part in the latest action.
The union is believed to be taking legal advice, but a PCS spokesman said it would rather settle the dispute by negotiation. "We are meeting Home Office management later today and hope that the officials have some flexibility so that we can have a reasonable dialogue. The problem over the past 18 months has been that there has not been the political will in the Home Office to reach a solution."
The 24-hour industrial action could disrupt immigration and customs services at Heathrow but it is likely to lead to only limited impact on passport control at the airports, as the Immigration Services Union, which represents some UK Border Force staff, is not taking part this time. The Identity and Passport Service, the Criminal Records Bureau and the London headquarters of the Home Office are also expected to face disruption.
The union has called for a programme of industrial action across the Home Office and its agencies running into the autumn in a dispute over compulsory redundancies, 8,500 job cuts and a two-year pay freeze.
