“Companies have figured out that if they outsource their recruiting and hiring, and what’s often considered to be the messy parts of their H.R. function, that they can then absolve themselves of any liability,” Ms. Ruckelshaus said. That hits low-wage minority workers the hardest because of “entrenched and persistent discrimination,” she said.

Kevin James, 29, one of the named plaintiffs in the suit, said he had applied for work through MVP on roughly 20 occasions but had been given a job only once. He sat in the MVP office waiting in vain while Hispanic applicants got assignments, he said.

On the one occasion when Mr. James was given a job, he said, he was sent to a packaging company where supervisors were hostile toward him, “hovering” over him and other black employees as they worked.

“It just seemed like a lot of tension, like they didn’t really want me to be there,” Mr. James said. He added that the staff of the MVP office in Cicero “was mainly Mexicans” and that the employees were not welcoming toward African-American job seekers.

“I’d say the whole staff was Mexican,” he said. “It was like the whole thing was built up mainly around Hispanics."

Rosa Ceja, 29, a former dispatcher at MVP’s office in Elmwood Park, Ill., said the company used a system of code words in an attempt to conceal its preferential treatment of Hispanics. She said her work often took her to the Cicero office, where the same system was in place.