OKLAHOMA CITY (AP) — A second federal lawsuit accusing a pair of Oklahoma business owners of luring immigrants to the U.S. on work visas then paying substandard wages highlights what some attorneys say is a prevalent human trafficking issue in the United States that seldom calls violators to task.

While there have been previous civil lawsuits over the treatment of immigrants in the United States on work visas, immigration attorney Kent Felty of Denver said they are and will continue to be rare, partly because of the language barrier immigrants face, their unfamiliarity with U.S. law, and the a...