The Central Bank has issued a warning about the firm Dean Witter Consultancy (USA), which it says is offering investment services in the country without authorisation.
It is against the law to operate as an investment firm in Ireland without the authorisation of the Central Bank.
The authority also said that customers who invest with such a firm are also not liable for compensation in the event of a problem.
The Central Bank issues regular warnings about unauthorised firms and maintains a list on its website.
