The Commerce Commission is investigating the decision by Auckland and Wellington international airports to reduce the number of duty-free operators to one.
Auckland International Airport announced in July last year that DFS Galleria would spend more than $18 million to redevelop and expand the range of duty-free storesat the airport in Mangere.
The Regency Duty Free contract has been scrapped, leaving DFS as the only operator from next year.
Meanwhile, Wellington Airport initially used DFS New Zealand as its sole provider.
Its lease is due to expire in mid-2009, so the airport held a tender process in 2006 for a new provider.
Regency Duty Free won the tender so the airport has been using both operators during what it calls a "transitionary process" until the DFS contract is up.
Commerce Commission spokeswoman Allanah Kalafatelis said it would not comment on a case once it was in the investigative stage but part 2 of the Commerce Act states that "a person that has a substantial degree of power in a market must not take advantage of that power".
They must not restrict the entry of a person into that market, prevent a person from competing in that market or eliminate any person from the market.
The act also states that no person shall enter into a contract that has the purpose of "substantially lessening competition in a market".
Auckland International Airport maintains that it has not breached the Commerce Act.
The company said: "The move from two duty-free operators to one operator will improve the delivery of duty-free retail services to the public at Auckland Airport by enhancing the depth and breadth of goods offered and make it a more attractive and competitive shopping destination relative to other international airports."
