Documents reveal the time frame Greater Wellington Regional Council deemed necessary to implement new rest and meal breaks for bus drivers across the country was slashed in half during negotiations.
The Transport Minister is confident the looming deadline can be met, but GWRC, a key player at the bargaining table for local authorities, can't rule out going back to the Beehive to ask for an extension.
They agreed on a transition period of 12 months following fears the new rules could not be implemented without cancelling thousands of bus services.
But a briefing letter for Transport Minister Phil Twyford shows GWRC originally asked for 24 months to make the changes.
It warned there would be "travel chaos" in Wellington and Auckland without a transition period.
GWRC chief executive Greg Campbell said in a statement all parties continued to work collectively towards the May 2020 deadline.
"The aim is to meet the deadline but councils have collectively warned that the process for operators, unions, central government agencies, regional councils and unitary authorities is challenging and expensive.
"While we are happy with the progress made to date, we have not ruled out asking for an extension to avoid service disruptions to customers across New Zealand."
GWRC chairman Daran Ponter said the Government had "miscalculated" how much needed to happen to implement the new rules and was dubious it could be done in 12 months.
"It means more drivers and it also potentially means more buses. Buses have to be ordered, drivers have to be trained.
"Even before you get to that point, the whole arrangement in relation to how meal breaks will be taken, what the breaks actually are, ensuring they fit with the legislation, all have to be negotiated."
Twyford said the breaks were about fairness and public safety, and a tripartite group had been set up to tackle long-term issues.
"I receive regular updates on the progress being made and there are several regional groups working on implementation.
"I'm confident that because of the commitment shown by all parties to work together, we will meet the deadline."
Auckland Transport appears to be in a better position than GWRC.
During negotiations, it did not specifically ask the Government for a 24-month grace period but requested an 18-month lead time to agree variations to contracts and to order and commission a new fleet.
An AT spokesperson said they were confident bus operators would implement fully compliant breaks by May 2020.
But Immigration and Workplace Relations Minister Iain Lees-Galloway has poured cold water on that.
"Before reaching to Immigration to fill labour shortages they need to be planning for their labour force needs, supporting Kiwis into jobs, paying decent wages and providing good conditions."
On the prospect of any extension to the rest and meal break implementation, Lees-Galloway said the agreement was bargained in good faith.
"I'd hope that the Council works hard to ensure they comply."