WASHINGTON — When a pharmaceutical company sold its patent rights for a blockbuster drug to an Indian tribe 16 months ago, stymied competitors and consumer groups condemned the move as a flagrant abuse of the patent system.

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.