The government can use its financial veto to kill a Labour Party bill that would extend paid parental leave from 14 weeks to six months.
MP Sue Moroney, who drafted it, says she's confident it has the numbers to at least get through its first reading because it has the backing of minor parties.
But if it gets as far as its third reading, when it would become law, Finance Minister Bill English is likely to invoke the financial veto which shoots down legislation which would have "more than a minor impact" on the government's books.
Labour Minister Kate Wilkinson says extending paid parental leave to six months would cost $150 million a year, and it's understood the government considers that to be more than minor.
Because it's running a deficit, the money would have to be borrowed and the government is trying to reduce debt as quickly as possible so it returns to surplus in 2014/15.
No decisions have been taken because the bill hasn't been discussed by National's caucus.
Ms Moroney has the backing of the Greens, Mana and United Future.
She's talking to the Maori Party and NZ First, and if she can get them all lined up the bill will have 61 votes - a single vote majority over National and ACT.
The financial veto can be used against a bill even if a majority of MPs want to pass it.
ACT's John Banks says $150m is unaffordable in the country's current circumstances.
"It doesn't make sense at this time to entertain it," he said.
Ms Moroney says her bill is carefully structured so paid parental leave would be extended gradually, reaching six months in 2014/15.