The Public Offices Commission has received a complaint about the holiday by the Tanaiste, Ms Harney, and the Minister for Finance, Mr McCreevy, in the French villa owned by the businessman Mr Ulick McEvaddy last August.
A spokeswoman for the commission confirmed yesterday that a complaint had been made under the Ethics in Public Office Act about a possible breach of Cabinet guidelines.
She said it could be a number of weeks before the commission determined if it was appropriate to carry out an investigation.
The matter was mentioned in the Dail last week by the Ceann Comhairle, Mr Seamus Pattison, who said he understood a complaint had been lodged with the Public Offices Commission on the matter.
The commission is made up of the Ceann Comhairle, the clerks of the Dail and Seanad and the Ombudsman, Mr Kevin Murphy.
The holiday resulted in major controversy, with allegations of conflict of interest by Opposition politicians. The Sunday Tribune claimed that weeks before the holiday Mr McEvaddy had met both Ministers to consider proposals for the development of a £150-million private rail line to Dublin Airport where he hoped to build a second terminal.
Both Ms Harney and Mr McCreevy have insisted that there was no conflict of interest.
A spokeswoman for the commission said last night it could not say who lodged the complaint. "That is a confidential matter," she added.