The Scottish FA has turned down a request to give Republic of Ireland fans extra tickets for next month's Euro 2016 qualifier at Celtic Park.
The FAI was given a minimum 5% allocation (3,209 seats), while applications totalled four times that.
A spokesman said the FAI "regretted" that the allocation was not increased.
"It is particularly disappointing that the Scottish FA is continuing to sell tickets on its website after they told us the match was sold out," he said.
"Many of these tickets are now being taken up by Irish supporters out of desperation, a situation that could be resolved easily by providing adequate numbers of away tickets in a designated Irish section of the stadium.
"We continue to call on the SFA to provide adequate numbers of seats for Irish supporters, and in the meantime will strive to find remedies for ticketless supporters where possible."
However, the Scottish FA said it had fulfilled its tickets obligation "in compliance with Uefa regulations".
"The match is now approaching a sell-out and we are releasing the last remaining restricted view seats via public sale to home fans," it added.
"Given the demand for tickets from Scotland supporters, and the need to comply with Uefa's safety and security regulations, we will be unable to increase the Republic of Ireland's away allocation."
The Republic go into the 14 November game second in Group D and three points ahead of Scotland.