"It is already normal practice for schools to close when non-teaching staff strike," said Ana Avoila at a news conference in Lisbon. "This strike has a very big impact in education.

"It will of course impact in health," she added, while stressing that a skeleton service there is guaranteed.

Other areas also set to be hit, Avoila said, include culture, where "many places... will probably close". The same went for tax and social security offices, which she said would suffer "major upheaval and in some places they won't be functioning."

Asked what proportion of union members would take part in this industrial action, Avoila predicted "good" participation, given some of the reasons for it: "in recent times ... workplaces have been with worse working conditions, personnel hasn't been taken on" and "there are places where the workers are [having to work] at a rate that they will be hard pressed to bear, if this continues".

While legally public sector employees are supposed to work a 35-hour week, she noted, in practice "many of them", above all in hospitals, end up working more, while "many work as many as 10 or 13 hours in a row". In addition, "we've had no salary increases since 2009 and our careers have not been unfrozen since 2005."

On how the Socialist government would react to the strike, she said that "the government has to be sensitive to this action" since striking is a last resort for workers.