The commission would be directed to ensure the Tauranga community was consulted on significant decisions and she hoped the council would be in a position to return to fully elected representation in the 2022 elections.
Five-term councillor Bill Grainger told the Bay of Plenty Times Weekend he was "quite gutted and floored".
In his view, Mahuta should have appointed a Crown manager and observer as the council had asked.
"If it was me in her position, what I would have done is for six months, got a Crown manager observer in to see how the council would grow and then make the decision if we need the commissioners.
"But to hit hard as she's done, and I'm sorry to say Nanaia, but that's the wrong decision in my eyes."
He had hoped to tidy up a few tasks such as getting a supermarket for Welcome Bay before retiring at the next election and saying goodbye to the council "but now the legs have been cut from underneath me".
Fourth-term councillor Kelvin Clout said he was "very disappointed that Minister Mahuta has engaged the nuclear option".
"The nine of us elected members were making good progress, enjoying a more collegial environment, and making sound decisions for our city."
He said any extension of the commission beyond October 2022 would be a "central government slap in the face for Tauranga's residents".
He said, in his view, aspects of the minister's public statement were confusing, including her hope that "elected representatives will work collectively to support the commission".
"It sounds like she still wants us to hang around unpaid to support them. People have to find another job or buy a business, as I'll be looking at. I'm not sure to what extent we can assist but I will do whatever is best for the city."
The minister said the elected representatives would remain in place until the appointment of the commission and she hoped they would "help ensure a smooth transition".
Once the commission is appointed, they technically remain in office but cannot perform their duties and are not entitled to pay.
Under the Act, the commission can appoint a member to a committee or subcommittee of the council, and they can be paid in that role.
Councillor John Robson was "not surprised" by the minister's decision.
He said the issue the minister raised about a lack of evidence of change in the council's response letter was one of the reasons he did not sign it.
"As has been pointed out by the minister, we failed to provide any evidence of any change in position. The failure to provide the evidence I believe was available was a failure by the governance of Tauranga City Council," he said, expressing his view.
Councillor Larry Baldock, a former MP, said he had been through events such as this - losing elections, for example - in his career before.
"You find a new way to get by." He had no plans other than to "enjoy Christmas".
He believed the minister made the right decision and in his view the council's senior staff deserved a "better working environment", while the city had needed a new direction for a long time.
Acting mayor Tina Salisbury said in a statement via the council she was "naturally disappointed" but respected the minister's decision and would help facilitate the transition.
She said day-to-day council operations would continue as normal.
The Bay of Plenty Times Weekend also contacted councillors Heidi Hughes, Andrew Hollis, Steve Morris and Dawn Kiddie for comment.
Stuart Crosby, president of Local Government New Zealand and former Tauranga mayor, said it was a "tough day" for the council.
"The commission will replace effectively the governance team. I am sure they are reflecting and hurting badly at the moment."
Crosby said clarity was needed over how the commission would operate, its scope and what role there would be for elected members in future.
Tauranga MP Simon Bridges has opposed the appointment of a commission but said now the decision was made "we must all make the most of it".
"I've personally made clear my doubts about it because removing democracy in this way will undoubtedly cause many unintended issues."
He said the Labour-led Government should be careful what it wished for.
Bay of Plenty National MP Todd Muller said the minister's decision was disappointing but not surprising.
"The minister now must appoint high-calibre commissioners who engage fully with our community and have the interests of the city front of mind."
Jan Tinetti, Tauranga-based Labour list MP, said she felt for the councillors but was excited for the future of the council.
She believed the commission could deliver "the strategic leadership that the people of Tauranga have been calling out for".
"We now have the opportunity to reset the dial."
Tauranga Chamber of Commerce chief executive Matt Cowley said it was never an easy decision to take away local democracy, but the minister had "no other option".
He said, in his view, the current environment would not attract mayoral candidates with the right skills and experience, so a reset was needed.
"Commissioners will still likely proceed with significant rate rises in 2021, but there is hope that the money raised will be better invested with the oversight of independent and experienced commissioners.
"The business community just wants progress. The show must go on."
The big question: What happens to the byelection?
The minister's announcement raised more questions than answers for some, including what will happen to the double byelection in progress in Tauranga.
According to her office, her decision to appoint a commission does not cancel the byelection. It will continue until the date the commission is appointed. She has said this will be in "early 2021".
"To keep the council, public and potential byelection candidates fully informed that the byelection will be cancelled when the commission is appointed, the minister announced her decision to appoint a commission now."
Nominations for a byelection to elect a new mayor and Ōtumoetai-Pyes Pa ward councillor are open until midday on Tuesday, with voting papers due to start being delivered on January 26 ahead of polling day on February 17.
Warwick Lampp, independent electoral officer for Tauranga City Council, said on Friday there was one nomination for each position so far. Nominated candidates could withdraw if they wished.
He said the byelection would not go ahead if there were no candidates when nominations closed.
If there was one candidate for a position, they would be automatically elected without a voting process but would be unlikely to be sworn into office before the commissioners were appointed.
If a position attracted multiple candidates, the byelection would continue as scheduled until commissioners were appointed.
The most expensive scenario for ratepayers would be multiple candidates for both positions.
The byelection would have to continue as legislated, costing the city up to $285,000 if voting closed before the commission was appointed - and the elected candidates would still be unlikely to be sworn in.
Former Tauranga mayor Greg Brownless, who has previously indicated he would stand in the byelection but has yet to make it official, said he believed the situation was a "mess" and he wanted a definitive statement from the Government about the date the commission would be appointed so candidates could have clarity about the process.
- Additional reporting by Leah Tebbutt