The Irish Nurses and Midwives Organisation is examining whether it can challenge the Croke Park pay cut proposals on grounds that they discriminate unfairly against women.
INMO general secretary Liam Doran said nurses and midwives who work off rosters have been unfairly singled out by cuts to premium payments.
He said prison officers and firefighters - unions largely comprised of men - got a better deal from the talks than the largely female health service.
Mr Doran said the union would look into whether the cuts are discriminatory in the coming days.
"The premium payments have been fairly static for the last 40 years. They are not now going to be uniform," he said.
"Whether that is stepping over the discriminatory boundary or not - we're going to seek an opinion on that."