The Irving, Texas, company said Saturday that it launched the probe after learning of possible fraudulent activity on some U.S. payment cards used at the home decor and crafts retailer.
Michaels Stores Inc. is working with federal law enforcement and data security experts, but has yet to confirm that its systems were compromised.
CEO Chuck Rubin suggests Michaels customers take steps to protect themselves, such as reviewing their account statements for unauthorized charges.
Neiman Marcus Group Ltd., recently said a security breach last year may have affected about 1.1 million cards.
Target Corp. has said hackers stole about 40 million debit and credit card numbers during the holiday season.