The INO and PNA, which represent the 45,000 nurses entering their sixth week of action in support of their claim for a 10.5% pay increase and a 35-hour week, - also plan three-hour stoppages at four major hospitals tomorrow, including Beaumont in Dublin and Naas General in Co Kildare.

The unions have also instructed their members to stick to rostered hours, which is tantamount to an overtime ban.

The escalation is a result of the HSE's threat to cut nurses' pay by over 13% from next Friday unless they agree to resume normal working.

A HSE spokesman yesterday confirmed that it will proceed to cut the nurses' pay, even though Taoiseach Bertie Ahern said on Friday that the HSE's move was "throwing oil on troubled waters".

"Our hand is being forced by the nurses' action and they have given us no option but to cut pay, " said Brendan Mulligan of the HSE employers' agency.

However, the INO informed the HSE that the union's legal advice is that the HSE's attempt to reduce pay is "unlawful and will be resisted with all appropriate means".

But the HSE said its move had been legally proofed.

Ahern has said he is prepared to bring in an international expert to look at how the nurses' working week could be reduced from 39 to 35 hours. But the taoiseach said this would have to be achieved on a cost-neutral basis, and that any pay claim would have to be resolved through the partnership process.

Liam Doran, general secretary of the INO, said he would examine the taoiseach's proposals but needed more detail.

Meanwhile, the Irish Hospital Consultants' Association (IHCA), which represents most of the country's 2,000 hospital consultants, has voted by over 90% to withdraw co-operation with hospital management, though they will continue to work as normal. The protest action, which the IHCA described as "modest", is over the HSE's decision to advertise for up to 68 consultant posts on a new contract which has not yet been agreed with the IHCA.

The rules of the IHCA prohibit consultants from engaging in strike action.