The complaint, to the ILO’s Committee on Freedom of Association, said the Thai government fails to enshrine in law the rights of its workers and trade unions, in violation of the internationally accepted principles of freedom of association set out in ILO conventions 87 and 98.

The legal action stems from a spontaneous two-day protest by off-duty Thai Airways staff from 18 January 2013 for a decent pay rise and bonus. Officials from the TG Union negotiated between the staff and management, and convinced them to end the protest. On 19 January the airline signed an agreement granting the pay and benefits demanded by the staff.

However, Thai Airways took legal action over the protest against four officials from the TG Union and in August 2015 a court ordered them to pay over USD9,000,000.

Gabriel Mocho, ITF civil aviation secretary, said: “It is shameful that Thai law is being used to punish union officials for their constructive and supportive behaviour. We now call on the ILO to step in and force the government of Thailand to legally protect the rights of its workers, and correct this rotten legislation, which is clearly in breach of international law.”

The union has pledged to appeal the ruling at Thailand’s supreme labour court.