The maker of the blockbuster medication Humira created a “patent thicket” to illegally maintain a monopoly over the drug so it could be sold at an ever-increasing rate to the U.S. market, a major union has claimed in a newly filed antitrust class action lawsuit.

UFCW Local 1500 Welfare Fund, which is the largest union of grocery store workers in New York state, filed the proposed class action lawsuit against AbbVie and numerous other companies Monday, contending that AbbVie abused the patent process and colluded with other drug companies to improperly stave off competition for Humira in the U.S. market.

The lawsuit was filed in the U.S. District Court for the Northern District of Illinois by attorneys from New York-based Labaton Sucharow, Chicago-area firm Freed Kanner London & Millen and Philadelphia-based Fine, Kaplan and Black.

According to the 84-page complaint, AbbVie applied for 250 patents to protect Humira, an anti-inflammatory that has made $130 billion in sales since launching 15 years ago, and used those patents to enter into anti-competitive settlement agreements with several other drug companies that allegedly guaranteed AbbVie would extend its monopoly over the drug until 2023.

“The sheer number of patents makes it 'nearly impossible for any biosimilar to feasibly litigate all of these patents,'” the union said in the complaint. “AbbVie has abused the patent system—collecting dozens and dozens of patents, many of which are overlapping and non-inventive—as a means to block competition in the U.S. market. It simply is not feasible for biosimilar manufacturers to engage in time-consuming and expensive patent litigation against this mass of dubious patents.”

The lawsuit comes less than a month after the U.S. Senate finance committee conducted a hearing into rising drug costs, questioning CEOs from seven major drug companies, including AbbVie. The complaint notes comments from senators who were critical of allegedly anti-competitive conduct that involves manipulating patents to preserve monopolies.

According to the complaint, the company that developed the antibody that makes Humira effective—which was later bought by an AbbVie predecessor—filed its patent application for the biologic in February 1996. At the time AbbVie's predecessor company, Abbott Laboratories, bought that company, the patent was set to expire in December 2016.

The FDA approved the drug in 2002, and, after that, AbbVie began to develop its “extensive 'patent thicket,'” the complaint said. The company filed 250 patent applications, and eventually obtained more than 100 patents, the complaint said.

The complaint, which alleges violations of the Sherman Act as well as numerous state antitrust and consumer protection laws, said AbbVie then used those patents to strong-arm seven competitors into “illegal” settlement agreements whereby the companies agreed not to introduce any generic versions of the drug until 2023.

The complaint also noted that the price of the drug has risen from $19,000 per patient after rebates in 2012 to as high as $50,000 per patient per year before rebates.

“AbbVie has abused the U.S. patent system in an illegal attempt to eliminate market competition for its drug Humira and keep prices sky-high,” Gregory Asciolla, co-chair of Labaton Sucharow's antitrust and competition litigation practice, said in a statement to the media. “With this lawsuit, AbbVie will have to open the doors to competition and compensate those who have paid exorbitant prices for their medication.”

The proposed class, according to the complaint, would be composed of those who indirectly purchased, or reimbursed for the drug since early 2017.

Adelle Infante, a spokeswoman for AbbVie, said in a statement, “Patents are essential to encourage and protect the investment required to develop advances in healthcare. Humira's innovative patents have repeatedly withstood challenges in legal proceedings. Our patent settlements, which do not include any payments by AbbVie, balance protecting our investment in innovation with access to biosimilars 10 years before our last Humira patent expires, and the allegations in the lawsuit are without merit.”

In an emailed statement to the press, a spokeswoman for Pfizer, one of the companies that entered into a patent settlement with AbbVie, said the company stood by the lawfulness of its agreement.

“We believe the lawsuit is without merit and that there are multiple grounds for supporting dismissal of the plaintiff's claims,” spokeswoman Sally Beatty said.