Costco Wholesale Corp (COST.O), Sam's Club (WMT.N) and a handful of other large retailers have disabled their online photo printing stores in recent days, on concerns about a possible data breach at PNI Digital Media, which manages and/or hosts photo services sites.

Last week CVS Health Corp (CVS.N) disabled its CVSphoto.com site, and the week beforeWalmart Canada's (WMT.N) walmartphotocentre.ca took a similar action after it was informed that customer credit card data had been potentially compromised.

Other photo printing sites that might have been recently affected included Rite Aid Corp (RAD.N) and British supermarket chain Tesco's (TSCO.L).

"We take the protection of information very seriously. PNI is investigating a potential credit card data issue, and outside security experts are assisting in the investigation," said Kirk Saville, vice president, global communications at Staples Inc (SPLS.O), which bought Vancouver-based PNI last year.

Some websites said they had been advised by PNI of a potential breach, while others said they acted because of recent reports.

Costco Canada and Rite Aid noted that PNI has limited access to customer information since it does not process credit cards, but the photo service sites were temporarily taken down as a precaution.

CVS and Walmart Canada asked customers to monitor their credit card transactions closely for unauthorized charges.

Tesco's page simply said it was it was unavailable for routine maintenance.

The retailers' main websites and other services were not affected by the potential breach.

Costco shares rose 0.2 percent to end regular trading at $145.04; Wal-Mart shares dipped 0.4 percent to $73.10; Rite Aid fell 1 percent to $8.82; Tesco shares ended 0.3 percent higher at 218.6 pence, and Staples shares eased 0.5 percent to $14.63.

By Solarina Ho - Reuters (Additional reporting by Nayan Das; Editing by Steve Orlofsky)