The John Muir Trust said the legal basis of the hearing into the development at Glenmorie in Easter Ross had been thrown into confusion by a landmark ruling in the Court of Session.
Earlier this month, Lady Clark of Calton ruled planning consent for the Viking Wind Farm in Shetland was unlawful on several grounds, including the fact the developer did not have an electricity generating license.
It has since emerged that AES Wind Generation, the company behind the Glenmorie development, is not a registered electricity licensee.
The Scottish Government is appealing Lady Clark's decision.
Helen McDade, John Muir Trust head of policy, said: "Until the legal position has been clarified there is no point in wasting up to £100,000 on a Public Local Inquiry. If the appeal court upholds Lady Clark's decision, the developer will have to resubmit its proposal from scratch, thus rendering meaningless the deliberations of the Public Local Inquiry."
A spokeswoman for AES Wind Generation said it was "standard" to apply for an energy licence after planning consent was granted.