The proposed 1.25 percentage-point reduction in companies' contributions is part of a deal reached by the government and employer organisations, as well as the UGT trade union federation, in December that would see the minimum monthly salary rise to €557 next year from €530 this.

Portugal's largest union federation, the CGTP, refused to sign the deal and the Communist Party has criticised it fiercely, casting it as a present to employees that will serve to undermine the finances of the social security system.

Earlier on Thursday, the opposition centre-right Social Democratic Party said that it favoured a parliamentary review of the measure and could vote with left parties to revoke it.

The UGT, meanwhile, expressed concern at the developments, saying that they represented a lack of respect for the statutory tripartite forum in which such issues are traditionally agreed in Portugal.