This month, the company, Allergan, doubled down, asking the Supreme Court to rule that the Saint Regis Mohawk Tribe can use its sovereign immunity to fend off challenges by makers of low-cost generic copies of the best-selling prescription eyedrops, Restasis.

Congress is gearing up for what promises to be a yearlong investigation of drug prices, with House and Senate committees planning to hold hearings on Tuesday. The deal between Allergan and the Saint Regis Mohawks promises to be front and center when lawmakers in both parties examine the use of patents to delay competition and keep prices high.

Restasis, a treatment of chronic dry eye disease, had sales of nearly $1.5 billion in 2017 — Allergan’s best seller after Botox.

In September 2017, Allergan transferred patents for the eye drug to the tribe in upstate New York. Allergan paid the tribe $13.75 million up front and agreed to pay up to $15 million a year in royalties as long as the patents remained valid. At the same time, the tribe gave Allergan “the sole and exclusive right” to manufacture and market the drug in the United States.

The company says it is trying to protect its “intellectual property.” The tribe says it needs the money to provide health, education, welfare, housing and other services for its members.

But Michael A. Carrier, a law professor at Rutgers University, said, “This has nothing to do with the purpose of tribal immunity and everything to do with evading the patent system.”

Generic drug companies have challenged the validity of the patents. And so far, the tribe has struck out in its efforts to use sovereign immunity as a shield for the patents.

Judge William C. Bryson of the U.S. Court of Appeals for the Federal Circuit said he had “serious concerns about the legitimacy of the tactic that Allergan and the tribe have employed.” He found that four of the Restasis patents were invalid.

Allergan and the tribe are now asking the Supreme Court to rule that the tribe can assert sovereign immunity in proceedings at the Patent and Trademark Office.