The Māori Party says it will rip up the confidence and supply deal with National if there are no changes to the proposed legislation for the Ministry for Vulnerable Children.
Co-leader Marama Fox says the ministry is not "Māori-centric" enough, despite 60 percent of kids in state-care being Māori.
Ms Fox says current provisions mean the ministry can avoid rehoming children with family, if they deem it to be too much work.
"We're not talking about putting a child back into an unsafe home -that's stupid. But just because it's a Māori home doesn't make it an unsafe home, and that's where we want to make it explicit in the law."
She wants a guarantee they'll be re-homed with extended whanau where possible.
"Those words are sort of in there, except they are predicated by provisos like 'where applicable', 'wherever practicable', and for us that just means somebody an out to say, 'If I haven't got the time, I won't bother looking.'"
Ms Fox says this is a bigger issue for her than the Kermadecs, which the party also threatened to ditch National over.
"I will fight for this every day of the week. If we get to a point where we can no longer agree, we'll cross that bridge when we get to it.
NZ First leader Winston Peters disagrees, telling Fairfax there's no place for a "whanau first" approach.
"I've known of too many children thrown from pillar to post between whanau members."