The Irish Medical Organisation (IMO) has warned that it will take "all necessary action" to protect the rights of non-consultant hospital doctors (NCHDs), formerly known as junior doctors.
It follows last week's announcement of a recruitment freeze by the Health Service Executive (HSE) which will impact NCHDs.
The IMO said the move would be a breach of NCHD contractual rights and will lead to dangerous conditions for patient care.
The union has met with the HSE and warned the recruitment freeze will lead to further pressure on staff, uncertainty over cover and will see more NCHDs leaving Ireland for positions abroad.
"At our meeting we advised the HSE of the chaos a recruitment freeze would cause for the health services," said Dr Rachel McNamara, Chair of the IMO NCHD Committee.
"We also strongly rejected the position of the HSE that the NCHD Agreement reached in 2022 could now be implemented in the context of a recruitment freeze," Dr McNamara said.
The IMO said it is awaiting a response from the HSE in terms of rescinding the freeze and will then be calling a national NCHD meeting to determine what action is required.
The HSE said there are a number of key frontline positions which are exempt from the recruitment freeze to ensure impact to services and patients is at a minimum.
"It important to note in relation to 2023, the HSE received 499 new jobs for consultants and NCHDs," a HSE spokesperson said.
"The HSE has now filled these new jobs and exceeded it," the spokesperson added.