Karin Grech Hospital is running at half its capacity because of a nursing shortage, the MUMN claimed on Wednesday.
In a statement, the union said that a further 14 nurses resigned over the past two weeks, with the hospital now 50 nurses short.
"Because of this shortage, out of 270 beds at Karin Grech Hospital, only around 140 are being actually utilised," the Malta Union of Midwives and Nurses said.
The shortage crisis had no limits and no boundaries, it lamented.
The union further claimed that had it allowed the health authorities to issue a call that would have poached more nurses from the private sector, the situation would have been "catastrophic". An MUMN spokesperson told Times of Malta that the shortage in the private sector was even worse.
The situation in the private sector is so dire that carers employed by the private sector to support nursing staff at hospitals across Malta, were moving to the UK "in a rapid mode".
The union said it was an open secret that Malta was a "stepping stone" for nurses and carers who spend two years here to gain experience and knowledge and then move to the UK for "much better salaries".
It added that every week, some three nurses were giving up their Mater Dei job to move to the UK.
"The Health Minister is more focused on the election campaign than on the crisis facing each and every hospital in Malta.
"On the other hand, the Health Division's Permanent Secretary (who the MUMN wants to resign) has already proven that his only concern is industrial disputes and he has never even tried to seek solutions to such nursing crisis."
It said that its repeated efforts to kick off talks for a new sectorial agreement that would stop nursing haemorrhages was being ignored by the minister and permanent secretary.
Their only "solution" was to poach from the private sector - something that could lead to a "serious catastrophe".
"While all EU countries embarked on addressing their nursing shortage by providing much better working conditions and increased salaries, the health ministry’s main concern is only the coming general election," it said.