VANCOUVER - A lawyer for BC Hydro says a stop-work order on the Site C hydroelectric dam would have a big impact on its construction schedule.

Mark Andrews has told a B.C. Supreme Court judge that construction on the northeast B.C. dam would be delayed by at least a year if an injunction is granted.

The West Moberly and Prophet River First Nations are challenging the nearly $9-billion project by arguing they were not properly consulted before permits were granted for the first stage of construction.

The Treaty 8 Tribal Alliance members say they will suffer irreparable harm if the utility is allowed to start clearing thousands of hectares of old-growth forest.

Andrews says a delay would cost more than $300 million and push back site preparation that is critical for awarding a primary contract for building the dam.

He says the project is in the public interest because the dam would eventually produce power for thousands of homes.