A group of nonunion contractors from Minnesota and North Dakota filed a federal lawsuit on Tuesday against Minneapolis Public Schools, arguing that the district is violating free speech and due process by hiring only union workers.

The contractors, represented by the conservative California-based Pacific Legal Foundation, said the district picks only union contractors for building projects, even when they provide higher bids.

The contractors argue that's discrimination.

"If the school district said that only Republicans or Democrats would be considered for a bid, that would be a First Amendment violation on viewpoint discrimination," said Wen Fa, a Pacific Legal Foundation attorney.

The district said it is reviewing the lawsuit. The union that represents many of the district workers, the Minneapolis Building and Construction Trades Council, denounced the lawsuit.

"We have a track record of building large economic impact projects on time and on budget and with a workforce that reflects the diversity of our state," said Dan McConnell, the Trades Council's business manager.

The Trades Council noted that nonunion contractors can also bid on Minneapolis school projects.

That's true only in theory, Fa said.

Even if nonunion contractors were awarded a project, they would still have to hire workers from union halls, he said.

The lawsuit says 24 states have banned the type of labor agreements used by the school district. Brendan Cummins, an attorney who represents the Trades Council, said Minnesota's appellate courts have upheld the agreements as legal.

The Pacific Legal Foundation has won two recent significant Minnesota cases. The firm backed a lawsuit that saw the U.S. Supreme Court throw out a ban on wearing political clothing at state polling places.

Earlier this month, the firm helped win a case in front of the Eighth Circuit Court of Appeals, which ruled that two boys could join their competitive high school dance teams.

Last year, the U.S. Supreme Court dealt a significant blow to labor unions, ruling that public employees who do not join unions cannot be required to pay for collective bargaining.

Brandon Stahl • 612-673-4626

Correction: Attorney Brendan Cummins represents the Minneapolis Building and Construction Trades Council. His client was misstated in earlier versions of this story.