The Metropolitan Council must release documents detailing the machinations that took place while the regional planning body was devising the route of the controversial $1.79 billion Southwest light-rail line, according to a federal court ruling Tuesday.

The order by U.S. District Judge John Tunheim is the latest twist in a nearly two-year-old lawsuit filed by a Minneapolis group called the Lakes & Parks Alliance (LPA) that seeks to block the project.

Tunheim gave the Met Council 15 days to hand over the records — “so long as those requests are not unduly burdensome.”

The documents would likely include e-mails, letters, correspondence and reports related to how the current Southwest route was determined.

The alliance’s suit, filed in U.S. District Court in Minneapolis, claims that the 14.5-mile line violates federal law because the route was chosen before a thorough environmental review was done.

The LPA group is particularly concerned about the project’s route through the Kenilworth corridor, a popular biking and pedestrian area that is part of Minneapolis’ Chain of Lakes. The line, connecting downtown Minneapolis with Eden Prairie, is slated to begin service in 2020.

The LPA requested documents last year related to the Met Council’s “commitments and negotiations with cities along the line,” but the council argued that the group was not entitled to the information and sought a protective order. That request was denied by a magistrate judge earlier this year — and on Tuesday, Tunheim affirmed that decision.

In a statement, the alliance claimed that the documents “will prove the Met Council has proceeded illegally” by committing to a particular route before a final environmental review, as required by federal law.

It is unclear when Tunheim will rule on the broader issues in the lawsuit. LPA spokeswoman Mary Pattock said that if he rules in the alliance’s favor, “the whole project would go back to ‘Go.’ ”

The Met Council was willing to release documents, but only those that were limited to the administrative record. In a statement Tuesday, spokeswoman Kate Brickman said that Tunheim “ordered that LPA is entitled only to tailored discovery on this matter. We will be working to identify and produce the relevant documents.”

Earlier this year, the Met Council characterized the request as a “fishing expedition” by a “small group of opponents.”

On Friday, the Federal Transit Administration published an environmental-impact statement assessing the project, one of the last regulatory hurdles before construction is to begin next year. The review found that the character of the Kenilworth corridor would change and that steps would be needed to mitigate the impact. That was the case with areas elsewhere along the proposed route, as well.

State’s $135M share stalls

Meanwhile, the final piece of local funding, totaling $135 million, is stalled at the Legislature, and the session ends on Monday. Gov. Mark Dayton and other transit supporters have proposed a half-cent sales tax in the seven-county metro area to help pay for Southwest and other transit projects. But Republicans have opposed any tax hikes.

The state share is needed for the Met Council to qualify for about $895 million in matching funds from the federal government.

The LPA said Tuesday’s ruling reinforces its position that “legislators should wait to fund SWLRT, at $1.8 billion the costliest public works project in Minnesota history, until the many policy and legal controversies surrounding it — including the LPA lawsuit — are resolved.”