MINNEAPOLIS -- Opponents of Enbridge Energy's (EEP.N) plan to replace its aging Line 3 crude oil pipeline across northern Minnesota have filed appeals to challenge the state Public Utilities Commission's approval of the project.

Environmental and tribal groups filed initial notices Wednesday with the Minnesota Court of Appeals against the commission's decision to grant a certificate of need for the project.

Filing a joint appeal were the Red Lake and White Earth Ojibwe tribes, Honor the Earth and the Sierra Club. Also filing was Friends of the Headwaters. Planning to file Thursday are the Youth Climate Intervenors, a group of teens and 20-somethings with official status in the proceedings.

Canada-based Enbridge (ENB.TO) says Line 3 is the most-studied pipeline project in Minnesota history, and that it believes the courts will reaffirm the PUC's decisions.