Experienced public school teachers who take five years off to have children will be downgraded to a beginner-teacher salary when they return to work under changes that the union says discriminates against mothers.

Under the NSW Department of Education's recent change to salary conditions, a teacher at the top of the pay scale who takes five years' leave to have kids and returns to work part time for three years would take 13 years longer to work back up to their pre-leave salary compared with a teacher who did not take the leave, says Anna Uren from the NSW Teacher's Federation.

They would also take a big loss in superannuation contributions.

"Somehow the Department keeps a straight face while saying that this is not an attack on the pay and conditions of women," Ms Uren said.

The Federation is considering taking legal or industrial action against the Department of Education over this and other changes made to the salary review process in May, which the union says were unilateral and will reduce women's salary and widen the gender pay gap.

"By paying very experienced teachers a beginning teacher's salary, this policy will drive them from the profession, completely undermining the priority to attract and retain skilled teachers into NSW public schools," Ms Uren said.

The new policy "contains salary penalties for teachers with broken career patterns [which are] more likely to affect women."

A spokesman for the department said that the changes were part of the Great Teaching, Inspired Learning reforms, which requires teachers to continually demonstrate competent teaching practices and professional development to maintain accreditation.

"The reforms aim to improve the quality of teaching and reward those teachers who achieve higher levels of professional accreditation, rather than the previous system, based upon years of service only," the spokesman said.

"All teachers who apply for a leave of absence from the profession – for any reason – of more than five years will need to demonstrate their competence by regaining their accreditation. This ensures the highest standard of teachers in NSW classrooms.

"A teacher on leave from the department can maintain accreditation by undertaking casual work in a NSW school and completing 100 hours of professional learning over five years."

Alexandra Heron, from the University of Sydney Business School's Women and Work Research Group, said while there were benefits to keeping in touch with the workplace while on parental leave, "it certainly shouldn't be done in a way that will make it more difficult for women to return to work at an appropriate level."

"Casual work is very hard to do with small children without adequate notice.

"The ABS figure for the gender pay gap in the whole education sector was 13.5% late last year, which is better than the overall average.

"You would hope that first of all the department would be keeping its own figures and secondly analysing changes such as these in terms of likely impact on the pay gap and how to mitigate that – and discussing this with teachers. We live in a society that values parental care in some ways, and in others like this it seems to undermine it. And it doesn't encourage men to care, which should be something they're actually thinking about."