In the United Kingdom, the Government Communications Headquarters (GCHQ) was a public-service entity charged with securing military and official communication. The staff of the GCHQ worked with secret information of vital importance to the national security of the United Kingdom. The prime minister was ex officio the minister of civil service. Since 1947, the staff of GCHQ had been allowed to join national trade unions. Between February 1979 and April 1981, GCHQ staff participated in industrial action that significantly disrupted the agency’s operations and caused a near shutdown of the office. In 1984 and in response to the earlier labor problems, Prime Minister Margaret Thatcher (defendant) issued an order in council (the order) prohibiting GCHQ staff from membership in national trade unions. The order was an act of royal prerogative made by the prime minister. The council of civil service unions (the unions) (plaintiff) sought judicial review of the order, arguing that to issue such a mandate without consulting the impacted parties was unfair and procedurally invalid. The trial court held that the order was procedurally insufficient because the prime minister failed to consult with the impacted employees before issuing the prohibition. The prime minister appealed. The court of appeal reversed. The unions appealed to the House of Lords, which served as the court of last resort at the time of the decision.