According to the prime minister's office, Costa was invited by ETUC’s secretary-general, Luca Visentini, and he is the only European prime minister taking part in the meeting.

The event will be attended by the president of the European Commission, Jean Claude Juncker, and the winner of the Nobel Prize in Economics Joseph Stiglitz.

Costa's speech will focus on “the European pillar of social rights and a social contract for Europe" and he will talk about his government's policies in the areas of labour and combatting poverty.

A government source said Costa would highlight "the need to implement a European pillar of social rights through a new social contract that responds to the citizens’ needs, giving them hope, confidence and security."

António Costa came into power in 2015 vowing to turn "a page of austerity" following several years of harsh austerity implemented by the previous centre-right coalition. His Socialist Party (PS) has been backed by the Left Bloc (BE) and the Communist Party (PCP) in parliament.

Portugal's government has been lauded for slashing the deficit and reducing unemployment while complying with Brussels' budget requirements.