Ohakune station sergeant Mike Craig said he became concerned after learning Fifield had been touting for security work without holding a licence. Under the Private Security Personnel and Private Investigators Act 2010, a person can be fined up to $40,000 if convicted of operating unlicensed, and a company can be fined up to $60,000.
A complaint was laid with the Department for Internal Affairs and a spokeswoman said evidence was being gathered on Fifield.
Detective Karl Reyland, of the Whanganui Child Abuse team, said it was a "concern for us that he is now trying to inject himself into an area where he would have contact with teenagers".
Bar owners contacted by the Herald on Sunday, who spoke on condition of anonymity, said they cancelled the contracts as soon as they learned Fifield was not licensed.
On Friday, Fifield confirmed he was providing security at Mardi Gras, but when asked if he held a licence, said he had passed the contract on to another company. He confirmed he lost his licence last year after his indecent assault conviction.
Fifield said the indecent assault came at a low time in his life, coming soon after his daughter had died.
"I was in a very bad state, mentally. It made me go downhill and I did one stupid mistake. It was a one-off event that happened, and I'm not that type of person."
Fifield denied he was using the music business to get access to teenaged girls.
"Theoretically, people shouldn't be underage in nightclubs so I can't see what you're trying to talk about."
Fifield said he was still likely to be at the Mardi Gras but not working in security.
"We'll probably be up there partying."
Organisers are expecting more than the 5000 revellers who turned up last year.
The event, now having its 20th anniversary, traditionally marks the opening of the North Island ski season.
Fifield said he had been working in the music industry for 10 years, putting on events including throughout New Zealand organising alcohol-free raves for teenagers.