Chick-fil-A has joined forces with law enforcement authorities and IT security experts to investigate a possible breach of its point-of-sale (POS) payment system after a number of financial institutions in the U.S. detected a fraud activity on payment cards used at the restaurant chain.

According to Brian Krebs, a credit card association alert issued before Christmas warning of a breach from Dec. 2, 2013 until Sept. 30, 2014 at a U.S. retailer likely referred to Chick-fil-A. Krebs also reported that a financial institution claimed 9,000 of its customers’ payment cards appeared in the alert, with Chick-fil-A POS purchases being the only ones shared by all.

The fast food retailer acknowledged that some restaurants had reported “potential unusual activity involving payment cards,” a statement said. If a breach is found “customers will not be liable for any fraudulent charges to their accounts.”  

UPDATE: Chik-Fil-A has confirmed its ongoing investigation into a possible payment system breach, issuing a statement and a lengthy FAQ on its website and pledging to issue more information on who is affected “as it becomes available.”