Data Protection Commissioner Helen Dixon has ruled against the Public Services Card (PSC) being used as a necessary form of identification for any services outside the Department of Employment Affairs and Social Protection.
The decision will call a halt to the use of the PSC as a form of national identity card though it will remain in use as an identifier in some cases.
The commissioner has also told the Department of Social Protection that it must delete any data collected in setting up a PSC card.
"The department does not have a legal basis for processing personal data when it's in the case of a person who's seeking to avail of a service with the public sector, other than the department itself," said Dixon.
"Any cards that have been issued, their validity is not in question by anything we've found in this report," she said.
"They can continue to be used in the context of availing of free travel or availing of benefits that a person is claiming from the department." Dixon said that the PSC can also be used by choice as proof of identity but this is now optional.
Under the ruling, no public-sector body can insist that service users acquire or present a card.
The Government position is that the card protects against social welfare fraud and identity theft.