After becoming aware of the issue, Auckland electoral officer Dale Ofsoske visited the CBD billboard in Hobson St and said "in my view it is an election sign".
Ms Crone also erected an election sign in Orewa, according to an Auckland Council spokeswoman.
"Ms Crone's options are to remove the signs or alter them so that they are not 'election' signs," the spokeswoman said.
Council democracy services manager Marquerite Delbet contacted Ms Crone by phone last Friday to explain the requirements of the bylaw and how the period for display applies to all election signs, including commercial billboards.
Ms Crone said she disagreed with Auckland Council's interpretation of the bylaw, was seeking legal and other advice and continuing discussions with council on the matter.
She said the billboards displayed "commercial advertising" and the sign in Orewa was for a public meeting with the local community.
"It's incredibly disappointing that council's wasting time and resource trying to restrict candidates from engaging with local communities," she said.
When Ms Crone announced she was standing for the mayoralty in December, she was sent a letter from the council advising her of the rules around electoral signage.
The letter provided a link to the election signs bylaw and stated "election signs may be displayed from the Saturday nine weeks prior to 'election day' until midnight the day before election day".
The maximum fine for not complying with displaying election signs outside the nine-week period is $500.
