Customers of An Post with prepaid Money Currency cards have been told by regulators that restrictions on the use of the cards cannot be lifted yet.
This is because the issuer of the cards has not been able to satisfy regulators that all client money is safe.
Last week, British authorities shut down the scandal-hit German payments company Wirecard, which is the issuer of the An Post Money Currency card.
In an update, the UK's Financial Conduct Authority (FCA) said it was maintaining continued pressure on Wirecard to resolve issues that would allow it to operate under certain conditions.
"However, we cannot lift the restrictions without reassuring ourselves that the firm has been able to satisfy all our concerns, for example, that all clients' money is safe. We hope to be able to issue an update soon," the FCA said.
Last week the FCA told Wirecard to halt its business after news that €1.9bn was missing from the accounts of the company.
Wirecard was told not to pay out or reduce any money it holds.
In a statement the British regulator said: "Our primary objective all along has been to protect the interests and money of consumers who use Wirecard."
There are 50,000 of the currency cards in circulation in this country, An Post says.
The company could not confirm the amount of money involved.
An Post said its Money Currency cards were marketed as an affordable way for customers to bring and use money abroad.
They are issued by the British offices of Wirecard Card Solutions Limited.
The cards cannot currently be used by customers in Ireland or abroad until further notice.
An Post has apologised for the mess.
"An Post greatly regrets this inconvenience to our customers and we are working to ascertain what impact this situation will have on customers who hold an An Post Money Currency Card. We will issue a further statement when more information becomes available," the State-owned postal company said.
No other An Post products, cards or services are affected by the restrictions.
The Money Currency cards have been suspended after the FCA froze the British operations of Wirecard, including Wirecard Card Solutions, on Friday.
The German parent company has collapsed with almost €2bn of assets unaccounted for and the UK operations of the company are no longer allowed to dispose of any funds, even the cash of customers.
On its website, the FCA said customers should contact Wirecard or their card provider directly and warned that Wirecard was not covered by the UK's Financial Services Compensation Scheme (FSCS) because it does not compensate customers of electronic money or payment services.
Wirecard in the UK has been obliged to hold customer funds separately from its own money under Britain's customer safeguarding rules.