A new report shows the gender pay gap widens once a woman becomes a mother.
The research commissioned by the Ministry for Women found women face a 4.4 percent drop in hourly wages compared to what they would have received if they didn't have children.
The gender pay gap has been closing since 1998 and is at its lowest since 2012, at 9.7 percent as of July 2017. However, it becomes larger among parents.
According to new research conducted by Motu Economic and Public Policy Research, men on average experience no significant decrease in hourly wages upon becoming a father, but the same couldn't be said for women.
The decrease in hourly wages was smaller for women who returned to work within six months, but those who took longer than 12 months to return to work saw an average decrease of 8.3 percent.
Women of all income groups were less likely to be employed after becoming parents, but low-income workers were most at risk.
Co-author of the report, Auckland University of Technology's Gail Pacheco said hours of work were also impacted by the length of time spent away from the labour market.
"After having children women who return to work in the first six months have 30 hours per week as their median number of hours, whereas this falls to 27 hours if they return in months seven to 12."
It fell to 22 hours if they returned after one year, she said.
Ms Pacheco said men's hours remained constant at 41 hours when they became a parent.
More flexible parental leave needed
Ministry for Women policy director Margaret Retter said the research could be used to inform women.
"One of the things it suggest is sharing those hours so that both partners take some flexible working arrangements. [It] is better than the woman taking all the time out themselves."
Ms Retter said there was action that government and employers could take to address this issue.
"Things like special training allowances to encourage women back in the workforce and to train in particular areas.
"And for employers offering things like flexible work which allow people to get back into the workforce more in their own terms."
Statistics New Zealand chief executive Liz MacPherson said she was fortunate enough to have flexible working practices available to her.
"My husband and I both shared parental leave between the two of us. We chose when we went back to work, we did a four day week each, [which] both of our workplaces were prepared to support us to do."
Ms MacPherson said the experience women gained from becoming a mother should be recognised by employers.
It should be a personal choice on how and if women returned to the workforce after childbirth, she said.