State utility regulators postponed a vote to approve a western Minnesota wind farm Thursday after construction unions criticized the project’s nonunion builder for primarily hiring out-of-state workers.

RES, a major renewable energy developer, last year proposed the Bitter Root wind farm near Canby with 44 wind turbines that could generate up to 152 megawatts of power, a decent-sized project. RES would both develop and build the wind farm.

The Laborers’ union, representing several construction unions, asserted that the socio-economic benefits of Bitter Root would be “substantially diminished” by a lack of Minnesota workers. RES has used nonunion trades workers on other wind farms in Minnesota, and the Laborers’ union says those workers were mostly from out of state.

The Minnesota Public Utilities Commission (PUC) decided the unions’ claims need a closer look.

The PUC tabled its vote on a “certificate of need” for Bitter Root, which is necessary for the project to move forward. Instead, the PUC voted 5-0 to make the project a “contested case,” which entails the appointment of a state administrative law judge in a court-like proceeding with the rights of discovery.

“This really requires contested case proceedings to examine the social and economic impacts of the project,” said PUC Commissioner Dan Lipschultz. The socio-economic effects of a new power plant are one of many factors that go into the PUC’s decisionmaking process.

Since a contested case can take a long time to make it through the system, Lipschultz and other commissioners urged RES and the Laborers to come to some sort of agreement on local workers, even if the project isn’t unionized.

The PUC has not commonly waded deeply into local hiring issues on renewable energy construction projects.

“It was bold step for them to take this issue seriously,” said Kevin Pranis, Minnesota and North Dakota marketing manager for the Laborers’ union.

As for RES, “We feel like this project has been singled out,” said Michelle Matthews, a senior development manager based in Minneapolis.

RES is headquartered in England. Its Colorado-based U.S. construction arm does have traveling work crews, “but we do try to do local job fairs,” too, Matthews said.

Matthews said Bitter Root wind farm will bring many benefits beyond employment. It will generate more than $700,000 annually in taxes that will go to counties and townships, while local landowners will collect over $1 million a year in lease payments for wind turbine sites, she said.

“That is a big part of the socio-economic impact,” she said.

RES is currently constructing another wind farm near Woodstock in Minnesota’s southwest corner.

Pranis said about 85 percent of the license plates on workers’ cars at the Woodstock job are from out of state.

“They take their national crews from all over the country and put them up in hotels,” he said.

A larger wind farm could require 150 to 300 workers, including heavy equipment operators, iron workers, carpenters and laborers. Usually, unionized wind farm construction sites also employ some “travelers,” though they are in the minority, Pranis said.

“We think [Bitter Root] is nothing more than a speculative development to enrich a foreign corporation at the expense of Minnesota workers,” he told the PUC. “It crowds out other potential wind projects.”

Union contractors, a significant force in Minnesota’s commercial construction market, have built several wind farms in the state, a national leader in wind energy. Nonunion contractors, though, have also built wind farms in Minnesota.

“We absolutely want our members doing the work,” Pranis said of the Bitter Root project — or any Minnesota wind farm for that matter. Still, he told the PUC the union would “have no objection” to a nonunion workforce on a wind farm project if it employed a majority of local workers.