MINNEAPOLIS (AP) — Sen. Tina Smith has proposed an amendment to force completion of a land swap needed for the proposed PolyMet copper-nickel mine in northeastern Minnesota, a move that drew criticism from environmentalists Friday.

The Minnesota Democrat plans to offer the amendment to a major defense policy bill that's expected to come up in the Senate soon. The text was published in Thursday's Congressional Record. Sen. Amy Klobuchar of Minnesota is listed as a cosponsor. The language is similar to a stand-alone bill by Rep. Rick Nolan, D-Minn., that passed the House last November. The legislation would circumvent four lawsuits pending in federal court that are aimed at blocking the land exchange.

The Sierra Club's national executive director, Michael Brune, urged top Senate leaders Friday to oppose Smith's amendment. In a letter to Majority Leader Mitch McConnell and Minority Leader Chuck Schumer, Brune called the land exchange a "sweetheart deal" for PolyMet that should not be fast-tracked while the courts consider whether the trade is legal.

The U.S. Forest Service approved the land exchange in January 2017. Under the agreement, PolyMet Mining Corp. would get 6,650 acres of federal land it needs in the Superior National Forest near Babbitt and Hoyt Lakes in return for about the same amount of private land that would be added to the national forest.

But environmental groups have filed four separate lawsuits to block the exchange, saying the deal undervalues the federal land and violates federal laws on land transfers and endangered species.

Paula Maccabee, an attorney for WaterLegacy, one of the groups that are suing, said in an interview that Smith's amendment is a "backroom effort" to circumvent the courts by attaching a rider to an unrelated must-pass bill without public hearings.

"It's so un-Minnesotan. This is not the way our great state usually works. We tend to be transparent. We tend to care about due process. We care about the environment," Maccabee said.

In an emailed response to The Associated Press, Smith's office said: "Sen. Smith is working to help get the land exchange done_which was approved and advocated for by the Obama Administration_and it would in no way undermine the environmental review process for the proposed mine itself. When it comes to PolyMet, the most important issue is that the project meets strict environmental requirements."

Opponents of both Polymet and a separate project called Twin Metals near Ely say they pose high environmental risks to pristine waters. Supporters of both projects say the mines can operate without harming the environment while providing hundreds of badly needed jobs on the Iron Range.