"The governability of the country is at issue, it’s true,” Santos Silva said in a break from a presentation on the programme of activities for the Day of Portuguese Language and Culture of the Community of Portuguese-Language Countries. “If we call into question the bases of the country's financial policy, it is clear that we jeopardise its governability.”

The minister said that he could not "understand how parties who have agreed with the PS [governing Socialist Party] for this government [and] approved proposals under this agreement, have had the PS give up important positions to adopt their proposals, can today jeopardise the sustainability of this solution in a negative coalition with the forces of the right."

The PS has governed since late 2015 despite lacking a majority in parliament, thanks to agreements it signed with smaller leftist parties. These voted against the government on the amendment on teachers’ service time.

"I also can't figure out how right-wing parties, who are always raising fears of alleged [state] bankruptcy, can cheerfully (...) adopt a measure that means eight hundred million euros per year in permanent expenditure," he added.

The prime minister, António Costa, on Thursday convened an urgent meeting of the government to review its political strategy, following the parliamentary defeat.

Parliament approved Thursday an amendment to government legislation, backed by all parties other than the PS, that called for nine years, four months and two days of teachers’ service time to be restored, as demanded by trade unions. The service time, which counts towards automatic career promotions, has been frozen for several years as a cost-cutting measure.

In comments on Thursday, the PS leader in parliament, Carlos César, said that this meant the current government setup was "unsustainable" and that the "unconstitutional" measure paved the way to the government possibly stepping down.