The National Party is supporting extending paid parental leave to 26 weeks by 2020.
"We'll support it. It will be good for mothers and babies," leader Bill English told TVNZ's Breakfast show.
"And I hope that they build in some of the flexibility that would allow both parents to take some periods of that at the same time."
Yesterday Cabinet approved the policy to increase paid parental leave to 22 weeks by July 1, 2018, and 26 weeks by July 1, 2020.
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Paid parental leave is now 18 weeks. The Government will meet the cost of increasing it and estimates it will cost $325m over four years.
English was finance minister last June when he vetoed former Labour MP Sue Moroney's bill to extend paid parental leave, saying it would put too much pressure on Government finances.
But he said the party always supported extending it when conditions allowed.
Prime Minister Jacinda Ardern said legislation will be introduced into the House tomorrow.
"This is a key part of our Families Package and one all three parties of government have been proud to support because it's the right thing to do.
"We want children to have the best start in life. Evidence shows having a parent at home as long as possible to care for a child provides a huge benefit for that child's development."
Ardern said about 28,000 parents get 18 weeks of paid parental leave - one of the lowest in the OECD.