Campbell, who claims his participation in the Beijing Olympics last year cost him NZ$121,000 (£47,000) - most of which came from his parents - opened a brothel with a friend in Auckland earlier this year.
Campbell went public with the scheme in July and the 23-year-old said he hoped to raise NZ$300,000 (£117,000) to alleviate any financial burden on his parents and to have more time to concentrate on training.
The NZOC has now written a letter to Campbell demanding he cease linking the Olympics to his business or face legal action.
A letter signed by Barry Maister, the secretary general of the NZOC, said: "Based on the Olympic values of excellence, friendship and respect, we would place your actions as totally inconsistent with these values.
"Your open solicitation of 'clients' for your 'business' while using the Olympic or Olympian connection must cease immediately, or the NZOC will be forced to consider taking legal action against you."
Campbell, who finished in the top 16 in the featherweight division at the Olympics in Beijing last year, defended his business and fund-raising efforts.
Owning and running brothels is legal in New Zealand, where laws governing prostitution are relatively liberal by world standards.
He said: "At the end of the day, I feel like I'm not exploiting anyone because no one has to be here, we are not forcing anyone to be here.
"They are here of their own free will."