National MPs will make a bid in Parliament to make paid parental leave more flexible, by allowing both parents to take time off together.

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The Labour-led government is currently pushing through a bill under urgency to extend leave from 18 weeks to 22 in July next year, then up to 26 in 2020.

The National Party blocked such legislation while in power, saying it was unaffordable, but then changed its tune in the lead up to the election.

The proposed law will be opened up for potential changes in Parliament this afternoon before its third and final reading later this week.

National MP Amy Adams said the party supported the bill, but would put forward an amendment asking for more flexibility.

"When you have a young baby, having the opportunity for parents to take some time off together can be an incredibly important step not only for allowing each of the two parents to bond with the child, but to allow them to support each other."

She hoped the government would allow the change but said it seemed to have been "closed off" to the idea to date.

Ms Adams said such matters could have been discussed by MPs at select committee, but Labour had skipped that step to speed up the process.

"They were of the view that they knew everything they needed to know and therefore didn't need to bother.

"It was their decision to rush this process through - so they will have to work out what their position is in the time that they've set."

She said it was a "missed opportunity" given the bill would not take effect until July next year.

"But we'll be doing everything we can to put that sort of workability or flexibility into the arrangement."

The Labour Party said it would not be supporting National's proposal to allow both parents to take time off together.

Workplace Relations Minister, Iain Lees-Galloway, said the amendment would actually shorten the period of time that the primary caregiver would have paid leave to spend time with their child.

He said he was not closing the door on the idea altogether, and may consider it in the future.

"I'm not opposing that amendment purely because it's come from the National Party, I'm more than happy to work with them, and in fact they have proposed another amendment that actually I am keen to work constructively with them on."

National is also likely to put forward an amendment to extend so-called "keeping-in-touch days" which allow parents to return to work occasionally without losing their benefit.

"At the moment you get about three hours a week after an initial period, and if we extended Paid Parental leave without the ability to have keeping-in-touch hours we would reduce that amount per week," Mr Lees-Galloway said.

"If [National] can come to us with a reasonable proposal on that before our caucus meetings ...we'll consider that one," Mr Lees-Galloway said.