Minneapolis Mayor Jacob Frey, St. Paul Mayor Melvin Carter, Attorney General Keith Ellison and numerous legislators and City Council members are calling attention to alleged labor violations at nonunion construction sites operated by local developers.

Political leaders issued a joint letter to United Properties, Solhem Cos. and Yellow Tree, all based in Minneapolis.

"A large number of non-unionized workers regularly face wage theft, dangerous working conditions, threats, and other human rights violations. We are aware that one in five construction workers experience some form of wage theft, most often low-wage immigrant workers and workers of color," leaders outlined in their letter, which has more than 30 signers.

Those practices can be traced to subcontractors who have been retained by the developers.

The announcement of the letter, made at a news conference Monday morning, is part of a so-called week of action by Centro de Trabajadores Unidos en la Lucha (CTUL), a nonprofit worker-led organization fighting for better conditions on job sites.

The joint letter said that at least eight criminal cases have been filed over the last four years over industry issues in the metro area. It also charges that many workers are misclassified as independent contractors or are paid off the books.

Last week construction workers went to the corporate offices of United Properties, Solhem Cos. and Yellow Tree to deliver petitions calling for the developers to join the Building Dignity and Respect Standards Council. Minneapolis-based BDC sets standards and monitors development in the interests of human rights.

United Properties is owned by Minneapolis-based Pohlad Cos., which also owns the Minnesota Twins.

"We take concerns voiced about subcontractors very seriously. Subcontractors on all company-affiliated projects are required to comply with federal and state labor, benefit, workers' compensation and wage laws," United Properties said in a statement. "If we learn of unfair labor practice accusations made against subcontractors who have worked on our projects, we investigate the accusations in close partnership with our general contractors, and, when appropriate, will stop working with certain subcontractors."

Representatives of Solhem and Yellow Tree could not immediately be reached for comment.

For the workers, the sites with violations can be dangerous, they said.

"There's a lack of safety and safety equipment," said Pedro Carbajal, a nonunion worker who lives in Roseville.

Carbajal, who works with CTUL, does painting, sheetrock and landscaping work.

"There's not really the right to take a break. ... There are no sick days," said Carbajal, who spoke through an interpreter.