Nurses have said they "feel bullied" by health service senior managers over calls to end industrial action as a second day of strikes began on Wednesday.
Thousands of outpatient appointments have been cancelled as around 9,000 nurses took to picket lines across Northern Ireland for a second day of strike action.
They are calling for pay parity with their colleagues in the rest of the UK and have expressed concern around safe staffing levels.
Royal College of Nursing (RCN) director Pat Cullen said that "the finger was being pointed" at nurses over the current health service crisis.
A total of 2,380 outpatient appointments have been cancelled across Northern Ireland's five health trusts, with over 200 procedures called off due to the strike.
Interim Chief Executive of the South Eastern Health and Social Care Trust Seamus McGoran said nurses were taking the strike action during the "busiest week of the year" and "it is probably the straw that potentially could break the camel's back".
Royal College of Nursing Director Pat Cullen said nurses "felt bullied by management".
"Managers started to speak out last night which for nurses was extremely disappointing. Once again the finger is being pointed at the nurses for the state of our health service, for the crisis that they find themselves in," she told BBC Radio Ulster's Nolan Show.
"I want to categorically say it's absolutely not the nurses fault. Nurses do feel bullied by people saying 'enough is enough' and that they should call off this strike action.
"The voice of nursing is trying to be heard loud and clear on behalf of their patients and those in senior managerial positions came out last night and tried to silence them again.
"That to them is tantamount to bullying and it's not acceptable. It's a very sad state of affairs that we find ourselves in this position."
She said the onus was on the Department of Health to arrange a meeting for negotiations after being sent an email by the department saying they were willing to meet "at any time, in any place this week".
Northern Ireland's politicians have vowed to introduce pay parity if the Stormont institutions are restored. Secretary of State Julian Smith has set a deadline of January 13 for the current set of negotiations to restore power sharing.
Further strike action is planned by the Royal College of Nursing (RCN) and UNISON for Friday and throughout the month if an agreement cannot be reached with the Department of Health.
The Department of Health has urged trade unions to return to talks. They broke down without agreement in December, when a fresh 3.1% pay offer was rejected by unions.
Mrs Cullen said the strike was "not all about pay", and until safe staffing issues were resolved industrial action would continue.
Mrs Cullen told the BBC that essential services were still being provided despite the strike.
"Our nurses are back in today providing life-preserving services, those services have been exempted whilst nurses are on picket lines.
"It's nurses coming off night duty, nurses coming in off their leave, and on their day off standing out in the cold and the rain speaking up for their patients, speaking up for our profession that they value and a health service that they value," she said.
"But our nurses, it must be very clearly stated, are in providing those life preserving services for their patients today whilst they are still on strike."
Mr McGoran said the trusts "completely support the staff in their legitimate claim for pay parity".
"We are not blaming staff for taking industrial action, we understand why they have taken the action they have taken," he told the BBC
"It is very important for staff to keep calm in this situation."
The Belfast Trust has cancelled 1,232 outpatient appointments and 113 inpatient and day case procedures, with the Northern Trust cancelling 138 outpatient appointments, 20 inpatient procedures and day cases and 28 endoscopy procedures.
In the South Eastern Trust 712 out patient appointments and 155 procedures have been cancelled, the Southern Trust has cancelled 45 outpatient appointments.
The Western Trust has cancelled 253 outpatient appointments.
All those affected by cancellations have been contacted by the relevant authority. Those who have not been contacted should attend their appointments as normal.
Emergency departments remain open, but are expected to be under greater pressure than normal.
A number of special needs schools had to close due to the lack of adequate medical cover.
The Northern Ireland Ambulance Service is unaffected as ambulance staff are not taking part in the strike.
The decision by nurses to take strike action is unprecedented. The strike in December was the first in the 103-year-history of the RCN.