ST. PAUL  — Minnesota Gov. Tim Walz said Tuesday that his administration will keep pursuing an appeal of an independent regulatory commission’s approval of Enbridge Energy’s plan to replace its aging Line 3 crude oil pipeline across northern Minnesota, siding with environmental and tribal groups in his biggest decision since becoming governor last month.

The state Public Utilities Commission approved the project last summer. Then-Gov. Mark Dayton’s Department of Commerce appealed that decision in December, as did several groups opposed to the project. The Minnesota Court of Appeals last week dismissed those appeals as premature and sent the dispute back to the commission for further proceedings. That move forced the Walz administration to take a stand by Tuesday after weeks of studying whether to continue to appeal or let the matter drop.

The Commerce Department argued under Dayton that Enbridge failed to provide legally adequate long-range demand forecasts to establish the need for the project, but the commission concluded the Calgary, Alberta-based company met its requirements. Other groups fighting the project say it threatens oil spills in pristine waters in the Mississippi River headwaters region where Native Americans harvest wild rice and claim treaty rights, and that it would aggravate climate change.

“When it comes to any project that impacts our environment and our economy, we must follow the process, the law, and the science,” Walz said in a statement. “The Dayton administration’s appeal of the PUC’s decision is now a part of this process. By continuing that process, our administration will raise the Department of Commerce’s concerns to the court in hopes of gaining further clarity for all involved.”

While Line 3 opponents applauded Walz for heeding the department’s concerns, Republican legislative leaders said the Democratic governor made a big mistake. Enbridge said it expects to ultimately prevail.

Enbridge wants to replace Line 3, which was built in the 1960s, because it’s increasingly subject to cracking and corrosion, so it can run at only about half its original capacity. It says the replacement will ensure reliable deliveries of Canadian crude to Midwest refineries. It’s already in the process of replacing the Canadian segments and is running the short segment in Wisconsin that ends at its terminal in Superior.ass