NEW YORK (Reuters) - LL Bean has been sued by footwear maker Skechers USA ( SKX ), which accused the clothing and outdoor gear company of illegally copying its shoes, which have sold in the millions.

According to a complaint filed late Monday in Manhattan federal court, the world's third-largest footwear company believes LL Bean's Freeport casual shoes infringe two patented designs for "heel cups" that surround the back of the foot.

Skechers called its designs "unique and eye-catching" because they use "graceful, sweeping, gently rolling lines and slopes" resembling the shape of a heel.

"Only after Skechers incurred the substantial risk and monumental expense of developing and promoting its shoes with these heel cup designs, and established that they had broad appeal, did LL Bean enter the market with its infringing shoe," Skechers said.

LL Bean did not immediately respond on Tuesday to requests for comment. Skechers' lawyers did not immediately respond to similar requests.

The lawsuit seeks unspecified damages, including triple damages for any willful infringement, and to stop sales of infringing shoes.

Skechers sued at a time many Americans concerned about inflation keep a lid on discretionary spending.

The Freeport shoes, sharing the name of LL Bean's Maine hometown, retail for $99 on LL Bean's website.

LL Bean is privately held, and was founded in 1912. Skechers was founded 80 years later and is based in Manhattan Beach, California.

The case is Skechers USA Inc ( SKX ) et al v LL Bean Inc, U.S. District Court, Southern District of New York, No. 24-05336.