The allegation that Mayor Len Brown had sex with his mistress in Auckland Town Hall's Ngati Whatua room has surprised the iwi.
A signed affidavit outlining the alleged incident was posted online yesterday.
The author's name was blacked out, but she has been widely identified as Bevan Chuang.
It alleges the two were "sprung" by a security guard while having sex in the room early last year. The guard apologised and left, Ms Chuang said.
"Mr Brown was also quite distressed, stating, 'This is it, this is it'."