ST. PAUL — Minnesota regulators have issued a formal order approving Enbridge Energy’s plan to replace its aging Line 3 crude oil pipeline across northern Minnesota, clearing the way for opponents to appeal.

The Public Utilities Commission voted in June to approve the project and filed its final written order Friday. Environmental and tribal groups plan to ask the Minnesota Court of Appeals to overturn that decision, and are now free to do so.

Alberta-based Enbridge said it needs to replace Line 3, which was built in the 1960s, because it’s increasingly subject to corrosion and cracking.

But opponents said the new line, which would follow a partly different route, risks oil spills in the pristine Mississippi River headwaters region where Native Americans harvest wild rice, and that it would aggravate climate change.