ST. PAUL, Minn. (AP) — 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 in northern Minnesota, siding with environmental and tribal groups in his biggest and most controversial decision since becoming governor last month.

The state Public Utilities Commission approved the project last summer, but 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 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.

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.

Walz, a Democrat, had been under increasing pressure to decide whether to fight Enbridge's plan even before the appeals court ruled. Just last Friday, faith leaders connected with Interfaith Power and Light gathered in his office to urge an appeal, and left gifts of wild rice for him and Lt. Gov. Peggy Flanagan, while a mostly Republican group of 77 lawmakers sent him a letter urging him to let the project move forward. Last month, a group of scientists went to Walz's office to say the project would worsen climate change by facilitating further use of fossil fuels.

When it dismissed the appeals, the court said the next step for opponents was to refile petitions for reconsideration with the commission. Because the commission has rejected all previous petitions to reconsider its major decisions on Line 3, it's expected to do so again and put the challenges back in the hands of the Court of Appeals within several months.

Reaction to the governor's decision was swift. Minnesota House Republican Minority Leader Kurt Daudt issued a statement saying Walz is "throwing up unnecessary roadblocks" to a project that will create jobs and generate property tax revenue.

"The Governor is choosing today to stand on the side of extreme environmentalists who occupy his office, shut down meetings, and commit felonies because they refuse to accept that pipelines are the safest way to transport oil," Daudt said, in a reference to felony charges filed last week against four activists connected with the Catholic Worker movement who acknowledged trying to close the emergency valves on another Enbridge pipeline in northern Minnesota.

Environmentalists welcomed the decision.

"Hundreds of young people have come to the Minnesota Capitol this month to tell Gov. Walz and the Minnesota Legislature that Minnesota Can't Wait for climate justice," Kathryn Hoffman, CEO of the Minnesota Center for Environmental Advocacy, said in a statement, referring to a protest last week. "Today, Gov. Walz showed that he's listening to them and that he is committed to using facts and science as the courts deliberate on the need for the Line 3 oil pipeline."

Enbridge called the decision "unfortunate" but said it will continue working with the administration to secure the necessary permits to begin construction while the legal challenges proceed.

"The Commission's approval came at the end of a thorough review of the facts, spanning four years, thousands of hours of environmental and cultural study, and substantial public comments. Enbridge believes the Commission will deny petitions for reconsideration as they have in the past," the company said in a statement.