The cyber attack occurred October 18 against Loyaltybuild, an Irish company that handles Coop's Hotellpremien program.
Loyaltybuild called the breach "quite sophisticated" and that all its clients "are being provided with full details of the impacted customers and how they were affected." Coop was told of the hacking Thursday night.
"Someone has got a hold of a data file. The information that we have now is that there are 143,000 customers affected, Coop's spokeswoman Louise Stephan told Swedish Radio. Stephan said if card owners discover something strange on their bill they should contact their bank.
On Thursday Coop sent an email to all customers using Hotellpremien but stressed no customers risked losing any money. The grocery store chain, owned by the Swedish Cooperative Union, has filed a police report on the IT breach. Swedish Radio reports police in Ireland have also launched an investigation.