Transport Minister Phil Twyford says he offered his resignation to the prime minister for making a phone call on a domestic flight after the aircraft doors had shut in preparation for take off.
While Jacinda Ardern declined Twyford's resignation, she has chosen to transfer his responsibilities for the Civil Aviation Authority (CAA) to associate Transport Minister Julie Anne Genter.
The issue came to his attention when National's transport spokeswoman Judith Collins wrote to him about it on Thursday.
Transport Minister Phil Twyford offered his resignation to Prime Minister Jacinda Ardern. She rejected it but transferred his responsibility for the Civil Aviation Authority to Julie Anne Genter.
Collins said she was told by a member of the public that Twyford had either made or received a call while a plane was taxiing at the airport. She said she followed up with a written question to see if there was any truth to it.
Twyford said he "hadn't given it a moment's thought until today".
"It's certainly not my habit to do this and it's very clear it's a breach of the rules and unacceptable. I'm not aware of ever having done it before," Twyford said.
The incident happened a week ago on the evening of Budget Day, when Twyford was on a flight leaving Wellington Airport.
"I made a mistake and I clearly wasn't thinking straight at the time. I recognise that and it was unacceptable and I apologise unreservedly."
Transport Minister Phil Twyford offered his resignation to Prime Minister Jacinda Arden for making a phone call on a domestic flight after the aircraft doors had shut.
Twyford said the call was to one of his staff members and lasted about one minute but nobody on the plane raised the issue with him.
He said Ardern "expressed her disappointment" when he told her about it.
In a statement Ardern said, "I expect all my Ministers to act in accordance with the rules. As Transport Minister it is even more important that Phil abides by civil aviation laws."
"It isn't appropriate for him to have responsibility for the Civil Aviation Authority in the event that it investigates this incident, so it's appropriate to transfer those responsibilities to Julie Anne Genter," she said.
In 2014 then-Transport Minister Gerry Brownlee was fined $2000 by the CAA after he bypassed security to board a domestic flight.
Brownlee also offered his resignation following the breach, but it was declined by then-Prime Minister John Key.
At the time Twyford said Key had been too quick off the mark in deciding not to accept Brownlee's resignation given the CAA hadn't completed its investigation.
"The Prime Minister did say that he was going to hold National Party ministers to a higher standard of accountability, so I would have hoped that the prime minister would have waited for the facts to be on the table about what regulations Mr Brownlee might have breached," he said in 2014.
Twyford said he felt his breach was similar to Brownlee's and he had written to the director of the CAA and expected the authority would take "whatever action it deemed necessary".
Former Minister of Police, John Banks, was also caught answering a mobile phone on a flight in 1991 and was fined $750.