"Teachers are not irresponsible, just like other Portuguese people are not and we lament that the prime minister uses such words to describe the legitimate ambition to progress in their careers according to the service they have provided," the trade union said in a statement.

The trade union added that it would continue to fight for teachers' careers to be valued and said it was "independent of parties and interests."

The rejection of the diploma by parliament came after the government last week threatened to step down if it was approved.

Public employees saw their salaries frozen during the financial crisis in 2011-2014. The government said it feared that if salaries were increased for teachers, other civil servants would request the same and its budget would be compromised.

Portugal's prime minister on Friday distanced himself from the possibility of the government resigning, saying the disapproval of the diploma was a victory of responsibility.

"It was a clarifying result and a victory of responsibility," he said.

The governing Socialist Party has been in power since late 2015, thanks to confidence-and-supply agreements with smaller leftist parties that, in this case, voted against the government.