Could the U.S. Supreme Court’s groundbreaking online sales tax ruling in South Dakota v. Wayfair spell trouble for the “king of qui tam”?

Illinois Attorney General Lisa Madigan has filed a series of motions to dismiss, which affect dozens of lawsuits filed by prolific whistleblower Stephen B. Diamond, alleging the cases have minimal financial and legal relevance for the state.

Madigan said the cases—targeting at least 70 tailors based primarily in Hong Kong, the U.K., and Thailand—involve sales tax disputes that don’t meet the economic presence thresholds established by the U.S. Supreme Court in its Wayfair decision earlier this year...