Papers have been filed in the Auckland District Court taking a private prosecution against mayor Len Brown.
Revelations in October last year of an extra-marital affair brought Mr Brown's spending under scrutiny and the Auckland Council subsequently censured him for failing to declare the use of 73 free or upgraded hotel rooms.
The case has been taken up by Wellington man Graham McCready, who says the documents he has filed under the Crimes Act allege bribery and corruption of a public official. He says they relate to accommodation upgrades worth about $5000.
"It may sound almost frivolous for $5000, but it's more than that. It's 50 times doing the same thing and not declaring them and it does undermine the whole system, and that's why the case has been taken."
The papers were filed by an associate of Mr McCready at the court about 4pm on Wednesday.
Mr McCready says Len Brown will now be contacted by the court and the process will take its course.
A spokesperson for the mayor says Mr Brown is aware of reports about the papers and is not commenting.
Electoral law experts doubt the private prosecution will succeed. Otago University law professor Andrew Geddis said showing Mr Brown received a benefit is only the first step towards proving the allegation while Wellington lawyer Graeme Edgeler said the case would be very hard to prove without witnesses.