In a statement from the Royal College of Nursing, Pat Cullen said:
Nurses across Northern Ireland are taking part in 24 hours of industrial action.
It means they will refuse to do any task that is not directly related to patient care.
Two days of further action by the Royal College of Nursing is also planned for Tuesday 10 and Wednesday 11 December with the first full strike on the 18 December.
It comes amid industrial action by Unison members which has seen thousands of outpatient appointments being cancelled this week.
Meanwhile members of Unite who work in the health and social care system voted on Monday night in favour of joining the strike the week before Christmas, on the 18th of December.
In response to the recent strike action, the Chief Executives of the six health trusts say ongoing industrial action could pose 'a significant risk to patient safety.'
They say a resolution to the current dispute is urgently needed, but recognise that it's difficult without a health minister and extra funding.
They said, "We accept that this is not possible without ministerial intervention and further resource. We now all need to urgently find a resolution to the current dispute."
The Health and Social Care Board has apologised to all those affected.
Northern Ireland Secretary of State, Julian Smith, has expressed his concerns at the impasse.