The National Party could face an embarrassing defeat on its major planning reforms unless it agrees to drop changes that affect genetically modified organisms.
The Maori Party, whose vote is needed to pass the reforms, opposes a change to the Resource Management Act (RMA) that will prevent councils from banning GE trials or releases in their regions.
The clause allows the Government to overrule councils not only on GMOs but on other activities related to the RMA.
Environment Minister Nick Smith refused to comment today, saying he wanted to "have discussions directly with the Maori Party".
But he has previously defended the provisions opposed by the Maori Party, saying councils could prevent important medical and scientific advances if they introduced GE-free policies.
The Maori Party has already secured significant concessions in the reforms, including a requirement for iwi to be involved earlier in the consent process in sensitive cases.
It supported the legislation at the second reading on Tuesday.
But co-leader Marama Fox said its ongoing support hinged on National amending the clause that related to ministerial powers.
She suggested that the legislation could include a "carve-out", which allowed the minister to over-rule other activities but not GMOs.
Auckland Council, Hastings District Council and Northland Regional Council have introduced GE-free policies.
Federated Farmers is challenging the Northland and Hastings policies in court.
CANDIDATE IN A TOUGH SPOT
The RMA reforms put Hastings Mayor Lawrence Yule in a tricky position.
He is National's candidate in the safe seat of Tukituki and is likely to enter Parliament this year.
But he has also championed his region's GE-free policy, which the National-led Government's reforms will block.
Yule said he stood by his council's position, but accepted his own view could have to change if he became an MP.
"I do have a view that is different to the party," he said. "If I happen to get into Parliament I will talk to the caucus about it."
Hastings District Council introduced the ban so its food producers could brand themselves as GE-free on the international market.