Democratic lawmakers are calling for Gov. Tim Walz to suspend all state permits for PolyMet's proposed copper-nickel mine in northern Minnesota, saying the state needs assurances "that the permits were not rigged."

It's the first move by lawmakers following recent disclosures about how state and federal regulators handled a crucial wastewater permit for PolyMet, which would be the state's first hard-rock mine. Three inquiries into that episode are underway.

Sen. John Marty, the Rose­ville Democrat leading the effort, said lawmakers were also motivated by Glencore's recent purchase of PolyMet Mining Corp. and the catastrophic failure earlier in the year of an iron ore mine tailings dam in Brazil, a facility with a similar design to the tailings dam PolyMet would use.

In a letter to Walz on Wednesday, the lawmakers asked the governor to suspend PolyMet's permits and to direct the Minnesota Pollution Control Agency to cooperate with inquiries into the permit scandal. They also called on regulators to modify the permit for PolyMet's tailings dam to a different design; get an "ironclad" financial assurances package with Glencore's name on it; and conduct a study of the mine's health impacts.

The letter is signed by 18 DFL legislators, including Marty. More signatures are coming, Marty said: "Our hope is to raise awareness about how serious this matter is."

Walz spokesman Teddy Tschann said the governor "takes these concerns seriously." He added the permit "is currently being reviewed in court, and he believes that process should continue."

House Minority Leader Kurt Daudt, R-Crown, called the letter an "ideological attack."

"It's disappointing that Metro Democrats are spreading misleading and false information about the environmental review process in an effort to derail this project and its tremendous benefits for Minnesota jobs and Minnesota's economy," Daudt said in a statement. "PolyMet is the most thoroughly reviewed industrial project in Minnesota history and has been going through the environmental review process for 14 years."

Any move to suspend approved permits would likely meet with resistance from Toronto-based PolyMet Mining and Glencore, the Switzerland-based mining giant that owns it. It holds more than 20 permits, most issued by state regulators. Construction will start after the company raises an additional $945 million, a process it estimates will take several months. The open-pit mine will be built near Babbitt on the Iron Range.

PolyMet issued a statement saying the project "meets all state and federal environmental standards, which are the most stringent in the nation and in the world. Multiple internal and external reviews, along with unprecedented public comment opportunities, have occurred on all aspects of the project, and it has been determined that PolyMet meets or exceeds all factors of safety."

Nancy Norr, chairwoman of Jobs for Minnesotans, said it's common to see mine opponents ramp up efforts before construction. She said she doesn't think Walz would suspend the permits because that would "fly in the face" of the long public permitting process.

DNR Assistant Commissioner Jess Richards said he cannot recall any similar requests to suspend a permit.

The Minnesota Pollution Control Agency (MPCA) provided a 13-page document showing how it addressed the EPA concerns with PolyMet's wastewater permit.

In a statement, MPCA Commissioner Laura Bishop defended the permit, called a National Pollutant Discharge Elimination (NPDES) permit. "With PolyMet's 479-page NPDES permit, the MPCA is holding the company accountable to stringent, enforceable water quality standards for eight contaminants, including mercury and lead," Bishop said. "I understand lawmakers' concerns, and welcome all opportunities to discuss the details of the permit."

MPCA Assistant Commissioner Katrina Kessler said it would be "very unusual" to suspend a permit. The MPCA "addressed" all of the EPA's concerns with the permit, she said: "We didn't do exactly what they asked for in each and every case."

Mine opponents said they were glad to see elected leaders get involved.

"The walls of silence are crumbling!" said Arne Carlson, Minnesota's Republican governor during the 1990s.

Kathryn Hoffman, head of the Minnesota Center for Environmental Advocacy, urged Walz to "hit the brakes" on PolyMet's plans.

"As our seven lawsuits show and these legislative leaders have recognized, the agencies charged with holding PolyMet accountable failed to do their jobs," Hoffman said in a statement.

Concerns about the rigor of the permitting process took a turn in January, when a retired EPA water lawyer from Boston, Jeffry Fowley, filed a complaint with the federal EPA Office of Inspector General. Fowley said he suspected misconduct in how Minnesota regulators and the EPA Region 5 office in Chicago, which oversees Minnesota's enforcement of federal pollution laws, handled PolyMet's wastewater permit. The permit regulates pollutants that can be discharged, such as mercury, arsenic and lead.

U.S. Sen. Betty McCollum and others began pressing the EPA for documents.

Eventually, the EPA released documents that showed career staffers at EPA Region 5 did not submit their criticisms of PolyMet's draft permit in writing, but read them over the telephone to Minnesota regulators. Then, a leaked e-mail showed that an MPCA assistant commissioner asked EPA Region 5 officials not to submit written comments during the open public comment period, effectively keeping them out of the public record.

Finally, a detailed memo by Kevin Pierard, chief of the wastewater permitting branch at EPA Region 5, was leaked. It documented nearly 30 concerns EPA had with PolyMet's permit and how many issues were not resolved.