Television presenter Matt Lauer and his wife, former model and Unicef ambassador Annette Roque, bought the lease to the 6468ha high-country station on the northern shores of Lake Hawea earlier this year.
The price the Lauers paid to buy the leasehold station from the Cochrane family has never been disclosed.
Soon after the sale was announced, several groups which had been involved in talks with the Lauers' representatives about better access through the farm to the Hunter Valley and the Hawea Conservation Park criticised the decision for not securing more meaningful access.
One of those groups, Federated Mountain Clubs, sought legal advice on the legitimacy of the sale and whether the Overseas Investment Act 2005 was properly applied.
President Peter Wilson told the Otago Daily Times he had a legal opinion that showed mistakes were made by the Overseas Investment Office when it applied tests within the Act to the sale.
Mr Wilson did not provide any more details about what parts of the decision were wrong and would not say if they would be taking legal action.
Overseas Investment Office spokeswoman Joanna Carr said the office stood by its decision to grant the sale of the station's lease to the Lauers and it had not had any communications with the FMC about any mistakes made in the decision.
After a decision had been made by the OIO, the only action that could be taken was a judicial review made under the Overseas Investment Act.
The Lauers' New Zealand legal representative, Graeme Todd, said he was surprised Mr Wilson would claim the consent was unlawful but not provide details.
There had been no approach from the FMC to the Lauers or him about any alleged errors in the OIO's decision, Mr Todd said.
Without any detail, it was impossible for the owners to respond to the FMC's claim, he said.
Since buying the leasehold station in March, the Lauers have made only one public comment.
In a statement, the couple said they looked forward to making a home at the station, being good stewards of the land and part of the Wanaka community.
As part of the sale, the Lauers committed to allow access over Sawyer Burn track and access to Sentinel Peak.
They will also pay for all the costs associated with legalising Mead Rd, which provides access to the Kidds Bush Reserve.
Access groups such as the FMC, the Upper Clutha Tracks Trust and Fish and Game all wanted guaranteed access into the Hunter Valley and to the 105,000ha Hawea Conservation Park.
Informal access through the farm is allowed but permission is needed from the Cochrane family, who have subleased the station back from the Lauers.
