Great River Energy is pulling out of the Big Stone II project completely. In addition, a second company, Southern Minnesota Municipal Power Agency, is re-evaluating its role in the proposed plant.
Great River Energy cited cost and environmental concerns, among other things, as reasons for its withdrawal.
The decision comes just a few weeks after the Big Stone II project cleared an important hurdle. In August, two Minnesota administrative law judges gave a favorable recommendation to a power line project needed for the plant.
Big Stone II communications manager Dan Sharp says the announcements could change the size of the facility.
"Most likely what we'll do is downsize the plant from the present 630 megawatts to probably around 500 megawatts," says Sharp.
Several groups have criticized the plan, saying it's economically and environmentally unsound.
Beth Goodpaster with the Minnesota Center for Environmental Advocacy says the action demonstrates the proposed power plant may be on shaky ground.
"We've been arguing that this is a risky project economically, and I think that when investors pull out late in the game like this that adds to that phenomenon," Goodpaster says.
Big Stone II would be built in South Dakota just a few miles west of Ortonville, Minnesota, next to an existing power plant.
The lead developer for Big Stone II is Otter Tail Power, of Fergus Falls, Minnesota. Ward Uggerud, senior vice president, said Great River Energy's exit does not change the need for new power and transmission facilities for the remaining utilities.
"The remaining utilities' load requirements show Big Stone II to be the least-cost option for meeting our customers' demand requirements even if we were to choose to downsize the project given these changes in participation," he said.
Uggerud said it's not uncommon for such changes in large, extensive projects, particularly during a long regulatory process.
The Minnesota Public Utilities Commission is the next agency to review the power line question, and the agency is expected to vote on the issue sometime this fall.
(The Associated Press contributed to this report)