The Government is seeking a High Court injunction to prevent border staff taking strike action on the eve of the Olympics, the Home Office has said.
It said the Government believed there was a "procedural error" in the ballot of members of the Public and Commercial Services (PCS) union and was turning to the courts to prevent the strike taking place.
It also repeated its calls for the PCS leadership to call off the strike ahead of the Olympics.
A Home Office spokesman said: "We believe that there was a procedural error in the PCS ballot and are therefore seeking an injunction at the High Court to prevent PCS taking strike action on Thursday.
"We want the PCS leadership to call off this irresponsible strike and we continue to ask members not to walk out at a time when the eyes of the world are on the UK."