The Revenue Commissioners, who are administering and collecting the tax, has confirmed to RTÉ News that it is treating the matter as attempted fraud.
An employee of Abtran, the company which handles the call centre for the property tax, has been suspended.
In a statement, Revenue said it understands that details in relation to 11 credit cards were improperly obtained by an unauthorised employee but no cardholder had suffered any loss.
It said the matter has been reported to the office of the Data Protection Commissioner.
The Revenue Commissioners established a telephone helpline when they announced details of how they planned to administer the Local Property Tax in March.
The contract to operate the helpline was won by a Cork-based call centre company, Abtran, which staffed it with 250 of its 1,100 employees.
Abtran was alerted by a caller to the helpline who became suspicious.
Gardaí have alerted the credit card companies involved, and they and the Revenue Companies are now attempting to make contact with the cardholders involoved.
Revenue will operate its own helpline for people with concerns from 9am tomorrow morning on 1890-226-336.
Abtran says it is satisfied that the activity was isolated to just one employee over a short period of time, and nothing like this has happened in the company's 16-year history.