The Department of Justice and Equality has processed just 10% of the applications it received in 2018 for grants under the immigrant investor programme.
In response to a parliamentary question from Fianna Fáil's Finance spokesperson Michael McGrath, the department said 420 applications were received as part of the scheme last year, of which 379 are currently being processed.
The department added a decision on a significant number of these applications is expected in the coming weeks.
The Immigrant Investor Programme was introduced in April 2012 to encourage inward investment to create business and employment opportunities in the State.
Since then over €500m has been granted to nearly 700 applicants, with more than half of the overall total handed out (€269 million) in 2017.
Commenting on the delay, Michael McGrath said: "It is a real concern that 90% of the applications received in 2018 under this scheme have yet to be processed by the Department.
"This points to significant administrative issues around the operation of the scheme. The Minister needs to give this issue personal attention to ensure that applications are dealt with promptly.
"This scheme brings valuable investment to Ireland but the reality is that investors have plenty of options as to where to invest their money and so decisions have to be made quickly," Mr McGrath added.