The Progressive Democrats say they want the amount of cash given to them by Ryanair to remain secret until next month.
A party spokesman said details of funding referred to by the Tánaiste, Ms Harney, during a Cabinet discussion last week would be revealed by the Public Offices Commission in its annual statement of political donations due for publication in the middle of March.
It was not intended to disclose the size of the donation by any other means, the spokesman said.
"There is a legislative framework for disclosure of donations and we comply with that. All details will be given in March."
Under the Electoral Act, political parties must declare all donations in excess of €5,000.
The PD spokesman confirmed the amount received from Ryanair in the past 12 months fell into that category.
Ms Harney asked the Government secretary to put the matter on record during a Cabinet discussion on the decision to approve new facilities at Dublin Airport for low-cost airlines.
The new "Pier D" development, to supplement the existing Gates A, B and C, had been sought by Ryanair chief executive, Mr Michael O'Leary, for some time.
Mr O'Leary wanted Ryanair to fund and build it, however, while last Tuesday's Cabinet decision leaves it in the control of Aer Rianta. Mr O'Leary has not yet commented publicly on the plan.
He is currently preparing for Thursday's inaugural Ryanair flight at Frankfurt Hahn airport, the company's fourth base on mainland Europe where it plans to run 30 flights a day on 10 trans-European routes.
A Ryanair spokeswoman said yesterday its busy schedule over the last week meant the management team had not had time to examine fully the implications of the Pier D decision or the consultant's report on which the decision was based.
She said they hoped to respond at the end of this week.