BETSI Cadwaladr University Health Board have put out a message to patients ahead of expected strike action next week.
Members of the Royal College of Nursing (RCN) in England, Wales and Northern Ireland took part in strikes on Thursday, December 15.
The second strike is set to go ahead on Tuesday (December 20).
In a statement, BCUHB said: "We anticipate that Industrial action will once again take place within BCUHB on, Tuesday, December 20 2022. We will provide further updates as and when necessary over the coming days. At present, our guidance on attending appointments and treatment remains the same: Patients due to attend an appointment or treatment at one of our sites on Tuesday, December 20 should attend as normal, unless told otherwise.
"There is no need to get in touch to check whether an existing appointment or treatment is going ahead on or around the day of action. If there are any changes or the need to rearrange we will contact patients directly with alternative dates."
According to provisional NHS data reported by trusts where the Royal College of Nursing (RCN) strike took place on Thursday, 2,452 inpatient and day case elective procedures and 13,327 outpatient appointments were rescheduled, coming to 15,779 in total.
The strike involved around a quarter of hospitals and community teams in England, all trusts in Northern Ireland and all but one health board in Wales.
The NHS was running a bank holiday-style service in many areas, though the RCN was staffing chemotherapy, emergency cancer services, dialysis, critical care units, neonatal and paediatric intensive care, alongside several other services.
RCN leader Pat Cullen has warned that action by nurses would escalate unless ministers back down on their refusal to negotiate on pay.
Over the Christmas period, visiting hours at Ysbyty Gwynedd, Ysbyty Glan Clwyd and Wrexham Maelor Hospital have been extended and will run from 10am to 8pm. Separate visiting arrangements are in place for those visiting maternity units.
BCUHB added: "Thank you for your understanding ahead of the planned industrial action and thank you to our staff for their dedication and commitment during this time."
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