Macy's is struggling to process credit cards in its stores, a painful setback as the retailer kicks off the holiday season.

"It is taking longer than usual to process some credit and gift cards," Radina Russell, a spokeswoman for the Cincinnati-based chain, said in an email. "But we have added additional associates to the floor."

Social-media users around the U.S. have complained the company's payment systems aren't working, spurring long lines and abandoned purchases.

The glitch marks the latest headache for a retailer that's trying to get back on its feet. Macy's has suffered 11 straight quarters of same-store sales declines, but Chief Executive Officer Jeff Gennette said earlier Friday that he was optimistic about this Black Friday — the traditional start to the year-end selling season.

The company is "working to resolve the issue as quickly as possible," Russell said.