MADISON, Wis. (AP) — A federal judge has temporarily blocked plans to build a high-voltage power line across a Mississippi River wildlife refuge, saying he wants to see documents detailing the lead-up to the project’s approval.

U.S. District Judge William Conley issued a preliminary injunction on Thursday preventing American Transmission Company, ITC Midwest and Dairyland Power Cooperative from beginning construction on a one-mile portion of the Cardinal-Hickory Creek transmission line that would cross the refuge. He extended the injunction indefinitely following a hearing in Madison on Friday morning.

The 345-kilovolt power line would run 102 miles (164 kilometers) between Iowa’s Dubuque County and Wisconsin’s Dane County. A section of the line would cross the Upper Mississippi River National Wildlife and Fish Refuge near Cassville, Wisconsin.

The refuge serves as a haven for fish, wildlife and migratory birds that use it as breeding grounds. It is the only stopping point left for many migratory birds that use the Mississippi Flyway. Conservationists fear the transmission line will damage the refuge and have been working for years to stop the project in court.

The National Wildlife Refuge Association, the Driftless Area Land Conservancy and the Wisconsin Wildlife Federation filed a federal lawsuit earlier this month. The groups allege the U.S. Fish and Wildlife Service issued final approvals for the refuge crossing in February without giving the public a chance to comment. They also argue that the agency and the utilities improperly reached a deal calling for the utilities to transfer about 36 acres (15 hectares) south of Cassville to the refuge in exchange for 19 acres (8 hectares) within the refuge for the power line.

The conservationists told the judge they needed an injunction quickly because the land deal was set to close Friday and the utilities have already positioned construction equipment on the edges of the refuge.

Attorneys for both sides sparred for about 90 minutes in front of Conley on Friday morning.

The conservationists’ lawyer, Howard Learner, told Conley that FWS released final documents this past February that found the land deal would have no significant impact on the refuge without offering the public a chance to comment on it.

He also argued that FWS never considered whether the power line would be a compatible use for refuge land as required by the 1997 National Wildlife Refuge System Act.

Reade Wilson, a U.S. Department of Justice attorney representing FWS, countered that the conservation groups commented on an environmental assessment of the project released in September and the agency was under no obligation to open up the no-impact finding for public comment. She went on to contend that the compatibility test doesn’t apply to a land exchange. Conley seemed incredulous, saying she was asking him to ignore that a power line would be running across the land.

In the end, Conley said he would extend the injunction until the parties provide him with a more extensive record of what steps were and weren’t taken during the run-up to the final approval in February. He said once the record was made available, the attorneys would have 30 days to submit briefs.

Outside of court, Learner said the conservationists were pleased to see Conley extend the injunction. The Driftless Area Land Conservancy and the Wisconsin Wildlife Federation issued a joint statement praising the decision.

“We should not set a precedent that a simple land swap is all it takes to plow through a national treasure,” Driftless Area Land Conservancy Executive Director Jennifer Filipiak said in the statement.

Wilson referred questions to U.S. Justice Department spokesperson Matthew Nies, who declined to comment.

ITC Midwest and Dairyland Power officials released a joint statement after the hearing saying the utilities disagree with the injunction. FWS acted within its legal authority under federal law and the line will help deliver reliable electricity from renewable sources to customers, they said.

The utilities added that they’re striving to minimize the environmental impact within the refuge, in part by avoiding any grading.

American Transmission Company spokesperson Jody Lau said in an email that the company finished its portion of the power line in December. She said the line is safe and reliable and the company looks forward to the full line going into service.