The INMO is defending its members after it emerged health workers and Gardaí take the most sick leave in the public service.
Figures published today show uncertified sick leave cost the economy €430m in 2012.
There are no figures available for last year, and new rules this year have cut the number of days allowed in half.
Liam Doran of the Irish Nurses and Midwives Organisation says they have a very challenging job.
He said: "I'm not standing over any malingerer, but equally, I am saying that in the world of work that I represent, there are stresses and strains, and with the patients in the bed, they want a 100% healthy person looking after them who has no risk of cross infection, no back strains.
"So there are explanations, but I'm not defending the malingerer.
"But I'm not going to apologise for nurses, midwives or other public servants who are legitimately out because of demands of their occupation."