The Commerce Commission has confirmed it is investigating real estate agents boycotting Trade Me.
Commission spokesman Gordon Irving said the situation with the real estate ads was of interest to the organisation.
"I can confirm the commission is investigating this issue. It is too early to determine the possible outcome of the investigation," he said.
Market analysts had previously raised the issue, saying real estate is a major source of revenue for Trade Me so the boycott would negatively affect the business.
The Herald has reported that a group of real estate agents said they would boycott Trade Me after the company announced price rises.
Some vendors have complained about their places not appearing on Trade Me as they wanted.
Trade Me chief executive Jon Macdonald said late last year that if Hamilton agents withdrew listings it would disadvantage property owners and that a listing fee of under $200 represented good value for money.
The commission enforces legislation that promotes competition and prohibits misleading and deceptive conduct by traders. It also enforces legislation that, through regulation, aims to provide the benefits of competition in markets where effective competition does not exist.
By Friday afternoon, more than 20,000 properties were advertised for sale on Trade Me. Listings included Northland 5974, Auckland 9701, Waikato 6722, Bay Of Plenty 4932, Wellington 3968, Canterbury 5141 and Otago 4003.
Trade Me expects to release its preliminary financial results for the six months to December 31 on February 19. Its shares are trading around $3.85.