The Health Service Executive has acknowledged that some services were disrupted in Cork, Portlaoise and Cavan due to a work stoppage by a number of agency nurses whose pay has been cut.
However, Director of Communications Paul Connors stressed that patient safety had not been compromised.
Mr Connors said that while 800 agency staff had turned up for work, a small fraction had not.
He said it was disappointing that some unions had advised agency staff not to turn up for work.
Mr Connors said he assumed there was a general acknowledgement that the HSE had to save money, adding that actions such as today's stoppage would only disrupt patient services and was unnecessary.
General Secretary of the Irish Nurses and Midwives Organisation Liam Doran said no one should be surprised that agency staff would make themselves unavailable to work when they were being treated as 'yellow pack' nurses.
Mr Doran criticised the HSE for implementing the new lower pay rates ahead of talks scheduled for this Wednesday.
He pointed out that while agency staff had previously had a higher rate of pay than direct employees, they had no job security pension entitlements or other benefits of permanent HSE employees.
Mr Doran also pointed out that the HSE had not cut the pay rates of hospital consultants hired through agencies.
However, the HSE said that was due to pressures of supply and demand in recruiting specialists in certain areas.
It said that some hospitals may have to postpone elective surgery because of the dispute.
At Cork University Maternity Hospital, 14 of the 16 agency midwives due to work at the hospital today made themselves unavailable for duty.
However, the hospital said that services were not affected today.
