Officials at Goodwill were first informed of the possible security breach Friday, and as of Monday have not yet been able to determine anything conclusive.
"At this point, no breach has been confirmed, but an investigation is underway," Goodwill Industries said in a statement.
"Goodwill Industries International is working with industry contacts and the federal authorities on the investigation [and will] work proactively with any individual local Goodwill involved, taking appropriate actions if a data compromise is uncovered."
Goodwill spokeswoman Joye Taylor told CNN Money that the organization has formed a response team that is actively working along side the Secret Service and federal payment card industry fraud investigative units.
"We are proactively engaged with the payment card industry contacts, the Secret Service and all Goodwill headquarters to identify what problem, if any, exists so that we can take prompt and appropriate actions as well as communicate appropriately to any affected parties."