Hadley responded to the email that evening asking for clarification about the meaning of "your" Christmas cards, and expressing concern the expenditure would not meet the auditor-general's guidelines.
"I have seen some that have a photograph of you, and it would not be appropriate for the ratepayers to fund a card promoting an individual, rather than the City," Hadley said.
Sir Tim called the question "existential" in a follow-up email and said proofs for the last 15 or so cards would be on file at the council.
Following a chairs meeting on Tuesday, it was decided the cards should come from both the mayor and chief executive on behalf of the organisation.
The card would also be produced as an e-card for the first time, with the savings going towards the mayor's Christmas dinner.
In response to Hadley's email before the meeting was held, Sir Tim argued the cards had so far managed to escape direct complaints from the auditor and suggested the mayor and chief executive don Santa and elf costumes as a show of unity.
"They became a bit of a collector's item. And boy did I get into trouble if I didn't send a card, or the person that I was sending it to had died," he told Local Democracy Reporting.
"It would probably be close to 100 [cards] I'd say. Part of the philosophy of bringing happiness and joy to Christmas time."
Speaking after the meeting, Sir Tim said the card dilemma had not created as much of a stir as he expected it would and sounded philosophical about the change of medium.
The card debate is the latest hurdle for Sir Tim, who claims his power has been stripped since reassuming office in October 2019.
Last month, the council did not pay his way to the Local Government New Zealand South Island conference in Christchurch, fearful he would not be able to represent it on issues such as Three Waters.
On Monday, he said a mayoral budget which allowed him to spend up to $40,000 a year on promotional projects had "vanished".
Sir Tim, 74, is in his ninth term as mayor of Invercargill and was previously mayor of Waitemata in Auckland.