The John Muir Trust is challenging a decision by Highland councillors to raise no objection against 67 wind turbines near Fort Augustus.
SSE Renewables has plans for up to 83 turbines at Stronelairg, near its Glendoe hydro electric scheme.
Councillors voted not to oppose the project if certain conditions were agreed, including a reduction in size.
The trust has lodged a petition in the Court of Session for a judicial review of the decision.
The landscape conservation charity opposes the wind farm, warning that it will “destroy the character” of an area of wild land.
Chairman John Hutchison said: “This legal action is not directed against the councillors, who have to deal with multiple issues and are forced to rely on expert advice from officials.
“We believe the quality of the advice itself was flawed and fundamentally in conflict with the existing local and national planning policy – which states explicitly that authorities should safeguard the character of wild land areas.
“Since the decision was taken, the Scottish government has confirmed the existing protection of wild land and proposed a further strengthening of wild land protection.”
In April, Highland Council’s south planning applications committee voted 11 to three in favour of raising no objection to the wind farm, if it was reduced in size and met other conditions.