According to a report presented to Thursday's Far North District Council meeting in Kaikohe, the initial estimate for fixing storm-damaged Far North roads was $27,280,000 but that has since risen to close to $40 million.
So far NZTA has approved $5 million for slip repairs with $1.2m pending; $1.5m has been approved to cover the initial response.
An email from NZTA stated the council should not assume that reinstatement would be to the roads' original condition.
Instead the agency was taking a "risk-management approach" that shared the risks of not carrying out full repairs with the council.
Northland MP Mike Sabin said NZTA's response was not his understanding of the Government's commitment. He also expressed surprise that the council had not contacted him.
"I'll be following it up with the Minister and the NZTA," he said.
Mayor John Carter said he was in discussions with Government ministers. A spokesman for Mr Brownlee's office said he would not comment because he was no longer Minister of Transport, and referred questions to new Transport Minister Simon Bridges. Mr Bridges' office referred questions to NZTA, which could not be contacted on Friday.
Councillors instructed chief executive Colin Dale to write to NZTA seeking clarification of the storm damage subsidy, whether roads will be restored to pre-storm condition, and who will be liable if an unrepaired road causes an accident. They also instructed Mr Carter to take up the issue with central government.
The council report showed NZTA will cover only 50 per cent of the cost of repairing the 49 most serious slips, leaving a shortfall of about $5 million. It will pay just over a third of the cost of repairing the 92 next most serious slips. Claims for the remaining 251 slips have yet to be lodged.
NZTA pays for repairs to state highways from a separate fund so Northland ratepayers don't have to cover major slips on SH1 and SH14.