Patagonia Inc, the high-end outdoor clothing retailer, filed a lawsuit accusing Gap Inc of illegally copying the "iconic" snapped flap pocket it has used on fleece outerwear for more than three decades.

​In a Tuesday night complaint filed in San Francisco federal court, Patagonia said Gap is willfully and deliberately selling fleece jackets that mimic its flap pocket and rectangular "P-6" logo without permission.

Patagonia said Gap's actions undermined its goodwill, and were intended to confuse shoppers into believing it made the jackets or let the retailer use its trademarks.

It also said it had warned San Francisco-based Gap in prior years to stop copying its products, meaning that the alleged "adoption of designs and logos bearing even more similarity cannot have occurred by accident."

The lawsuit includes a one-star review posted online by a Gap customer who called a Gap product an "Obvious Pata*gonia ripoff. I had to zoom in just to ensure that the logo was GAP."

Gap did not immediately respond on Wednesday to requests for comment.

The lawsuit seeks to recoup lost profits and unspecified damages, and halt further infringements.

Patagonia said it introduced its Snap-T pullover fleece in 1985 and added the flap pocket four years later.

It said the Snap-T design has been included in exhibitions at New York's Museum of Modern Art and London's Victoria & Albert Museum.

Patagonia is privately-held and based in Ventura, California. It sued Walmart Inc last month for allegedly infringing its trademarked logo of a trout.

The case is Patagonia Inc v Gap Inc, U.S. District Court, Northern District of California, No. 22-07437.