In a case at Edinburgh's Court of Session, Lafarge Aggregates is seeking to clarify whether a previous planning permission would allow a 600ha quarry to be established at Lingerbay on the Island of Harris.
Lafarge has been seeking to re-establish a quarry on the site since 1991.
At this week's hearing it is asking the court for clarification of the size and scale of an existing permission to quarry the side, granted in 1965.
But the Scottish environmental lobby is opposing the proposal. Organisations including Friends of the Earth (FoE) Scotland, Sustrans and WWF Scotland have come together to form the Link Quarry Group to fight the plans. FoE Scotland chief executive Duncan McLaren urged Lafarge to "do the decent thing" and withdraw its plans.