Minnesota is asking a federal judge to stop planned construction on a $2.1 billion Red River flood diversion project that has pitted the state against the U.S. Army Corps of Engineers, North Dakota and Fargo-Moorhead.

It’s another escalation in a contentious disagreement over one of the largest public works projects on the federal drawing board, one already bogged down by years of legal challenges. The fight has set communities up and down the river against each other over who would be protected from flooding and who would be flooded out as a result.

The state Department of Natural Resources on Thursday petitioned to join a pending federal lawsuit against the project, and Commissioner Tom Landwehr said that if the request is granted, the state will immediately ask the presiding judge to issue an injunction halting construction that otherwise could begin as early as January.

The project, which includes a ring dike around the three small North Dakota towns, a 36-mile diversion channel and a high-hazard dam, is designed to protect Fargo and Moorhead from the floods that have inundated towns up and down the Red River Valley for 51 out of the past 113 years.

Earlier this year, Gov. Mark Dayton said the state would not grant the permit to build the dam because it’s a significant safety risk, it’s not in the best interest of the state (Minnesota would lose thousands of acres of farmland while North Dakota would gain land for development around Fargo) and it would violate Minnesota’s environmental laws. The DNR wants to explore other options for flood control.

But the Fargo-Moorhead Diversion Authority, the legal entity behind the project, said that the U.S. Army Corps of Engineers has federal approval, and does not need the state permit. It is moving forward with the project on the North Dakota side of the river.

Earlier in December, the corps tapped a Minnesota company for a $46 million construction contract on a concrete flood-control structure that would regulate the flow of floodwater into a 36-mile channel around Fargo.

“It is our assertion that the permit is required to start construction even in North Dakota, ” Landwehr said.

Fargo Mayor Tim Mahoney, a member of the Diversion Authority, said Thursday that he is disappointed in Minnesota’s action. He said that the authority has been in discussions with the DNR and that construction wouldn’t start in Minnesota until 2019.

“We are trying to find a resolution,” he said.

Landwehr, however, said those discussions over a “Plan B” flood plan for Fargo-Moorhead are pointless as long as construction on the project is continuing, he said. An injunction from a federal judge would ensure that those discussions are conducted in good faith, he said.

It’s not the first time that Minnesota has gotten involved in the lawsuit. Earlier this year, the Eighth U.S. Circuit Court of Appeals upheld a ban on the construction of the ring dike around the North Dakota towns of Oxbow, Hickson and Bakke until the DNR made a decision on the dam permit.

In that fight, the state had petitioned to be a friend of the court. Now it is asking to join the plaintiffs in order to be a full-fledged party in the dispute before U.S. District Judge Jack Tunheim.

The other plaintiffs are counties and communities upstream from the dam that would be flooded as a result of its construction.

The diversion plan calls for thousands of acres in Minnesota to be flooded by newly constructed dams. But across the river, many more thousands of acres would be left high and dry and ripe for construction of homes, schools and businesses. North Dakota would pay $1.2 billion of the cost and Minnesota would pay $100 million.

And so far, while Congress has approved the project, it’s only provided $5 million of the $450 million in federal funds that are part of the deal.