A New York union filed a class-action lawsuit against AbbVie and seven other drugmakers, accusing them of throwing up a “patent thicket” to keep cheaper rivals to AbbVie’s blockbuster drug Humira off the market.

The health care plan of the New York local of the United Food and Commercial Workers Union says that patent settlements with Amgen, Samsung Bioepis, Mylan, Sandoz, Pfizer and some of their subsidiaries has artificially inflated the cost of Humira (adalimumab), an injectable biologic used to treat everything from rheumatoid arthritis to Crohn’s disease.

Humira is the world’s best-selling drug, with more than $130 billion in sales. It was worth nearly $20 billion to AbbVie, more than 60 percent of the company’s revenues last year alone.

The lawsuit, filed in federal court in Chicago, alleges numerous violations of federal and state antitrust laws. It says that AbbVie’s patent trolling will keep cheaper versions of Humira out of the U.S. market until at least 2023.