The opinion had been requested by the Ministry of Health, after midwives and other specialist nurses on maternity wards started a protest earlier this months that has brought some wards to a halt.

The document recognises that nurses have a right to defend their interests, for example by taking strike action, but stresses that “the refusal to provide nursing services as a specialist does not fit in the framework of a strike" and states that "failure to provide [due] service means unjustified absence" from work.

If a nurse refuses to exercise functions that form part of their specialist professional category "on the basis that there is no pay differentiation" - the essence of the protestors' complaint - they can and should be disciplined, the opinion states. It also notes that they could be sued for damages caused to patients as a result of not providing these services.

On the subject of the Order of Nurses - which has supported the protest from the start - the written opinion stressed that the organisation is not a trade union and so cannot call a strike.

Portugal's minister of health, Adalberto Campos Fernandes, earlier described the protest as irresponsible and outside the law, arguing that its aim is the “creation of social alarm”.

He said that the government would do all it could to maintain the quality of hospital services

Midwives and other specialist nurses on maternity wards have since the start of the month been protesting against the failure to pay specialist bonuses, by refusing to provide anything other than general nursing care. The Ministry of Health has in the meantime sought an urgent legal opinion from the attorney-general's office on the legality of the protest, which is still awaited.