Ashley Johnson, 22, a former employee at Brixx Pizza in Charlotte, said she was upset about a couple who stayed in the restaurant for 3 hours, forcing her to stay an hour past quitting time, and tipped her only $5, The Charlotte (N.C.) Observer reported Monday.
"Thanks for eating at Brixx," she wrote, before using profanity and calling the customers, who were not identified in any way in the post, "cheap."
Johnson said managers called her a day or two later and told her she was being fired for violating company policies against speaking ill of customers and depicting the restaurant negatively on social networking sites.
Johnson said she takes responsibility for her actions but does not believe she should have been fired.
"It was my own fault," she said. "I did write the message. But I had no idea that something that, to me is very small, could result in my losing my job."
Jeff Van Dyke, a co-owner of Brixx, said the policies are important to the company's image.
"We definitely care what people say about our customers," he said.