An "immediate review" is being undertaken into the working conditions and treatment of nurses at a hospital in Bangor.
It comes after Rhun ap Iorwerth, Senedd Member for Ynys Môn, called for an independent probe following revelations made by nursing staff at Ysbyty Gwynedd.
They include claims of workplace bullying, increased pressure for nurses to move from specialist areas to other wards and departments placing patients "at risk".
They also said they had to endure "unreasonably long working hours, poor relationship with management resulting in low morale" which is causing many staff to leave.
One nurse, who asked not to be named said: "Burnout is at an all time high at the site amongst nurses and other healthcare workers, and staff morale has never been so low. Many have chosen to leave their posts.
"We already work long hours and then feel pressured to take on more shifts - often redeployed to areas where we do not specialise - to help with staffing shortages.
"It is impossible to possess a high standard of nursing knowledge for every speciality that an individual could be covering from one day to the next. The situation has been escalating for years and has now reached a crisis stage with no solution."
Today, Jo Whitehead, chief executive of Betsi Cadwaladr University Health Board, said: "We are taking these concerns very seriously and are undertaking an immediate review into them."
Mr ap Iorwerth, who is also Plaid Cymru's spokesperson on health and care, raised the matter with the health minister, Eluned Morgan in the Senedd last week, prompting many nurses to come forward to share similar experiences.
Amongst the correspondence received, many nurses confirmed they had left posts at Ysbyty Gwynedd or the profession entirely, and many were considering leaving.
Ms Whitehead's statement continued: "We are committed to ensuring that all staff feel safe to raise concerns in a way that enables us to improve as an organisation and as an employer.
"Having listened to staff feedback, we recently introduced a new Speak Out Safely process, supported by a range of mechanisms to enable staff to raise issues anonymously but also enabling us to communicate with them to ensure they can be clear on what is being done to address these concerns.
"It is clear that not all staff feel that it is safe to speak out. It is important to us that we continue to improve the confidence of colleagues that their concerns will be addressed in a constructive way."