The Supreme Court is to hear an appeal over King Salmon's plan to expand its salmon farms in the Marlborough Sounds.
King Salmon wanted to put nine salmon farms in a protected part of the Marlborough Sounds but a board of inquiry rejected five of the sites.
The High Court in August rejected an appeal by Sustain our Sounds and the Environmental Defence Society against approval for the remaining four salmon farms.
Environmental Defence Society spokesperson Gary Taylor says the group has narrowed its objection to just one site at Port Gore.
"The board of inquiry found that the Port Gore site was an outstanding landscape. We argue that it should, having made that factual finding, have refused consent."
Mr Taylor says the decision to allow farms at four sites created an undesirable precedent because of its narrow interpretation of the New Zealand Coastal Policy Statement.
Save Our Sounds is also appealing against the High Court decision on the remaining three sites.
King Salmon chief executive Grant Rosewarne says the battle, which has cost $10 million over two years, is in complete contrast to the experience of salmon farmers in Tasmania.
"They've granted a larger expansion than ours at a fraction of the cost and are already under way and building it out. Salmon farming has been embraced by a Green-Labour coalition in Tasmania, and yet we're getting objections for what is one of the most sustainable ways of producing animal protein on the planet."
The case will be heard in the Supreme Court next month.