Nearly 6,000 HSE staff are currently absent from work, according to new figures.
The data obtained by Aontú shows that just over five per cent of staff, ranging from midwives, to doctors to dentists, are not showing up for work.
Stress and working conditions are being cited as the main reasons for the unusually high level of absenteeism.
Aontú Leader Peadar Toibín says that staff shortages are potentially putting patients' lives at risk.
Speaking to Newstalk, he said: "There's a clear correlation between low numbers of staff on wards and the ability of staff to be able to do their jobs properly."
"There's actually a very clear link between negative outcomes and adverse incidents in hospitals when staff are run off their feet and they don't have enough staff to go around."
1.5 million days lost
'Patient and client care' had the highest rate of absenteeism, at nearly eight per cent, while medical and dental absences were the lowest, at 1.7%.
Across all areas, 14% of those absent said that they had COVID-19.
"There are 1.5 million days lost a year and that's double the rate of absenteeism in the general population", Mr Tóibín said.
"And it's actually 50% higher than the absenteeism that's experienced in the NHS."
Under the HSE Managing Attendance Policies, an employee is not obliged to disclose the reason for the illness.
Staff who are absent from work due to sickness or ill health for more than two days are required
to submit medical certificates.
Pressure
Doctors are not required to state the nature of the illness on the medical certificates.
"It's having major problems throughout the health service", Mr Tóibín said.
"It's putting pressure because operations are often cancelled, treatments are often cancelled."
"The staff that are remaining have to pick up the pressure."
Main image shows a sign for the Irish Health Service Executive (HSE). Picture by: Stephen Barnes/Alamy