The current issue around the mandatory hotel quarantine system is not capacity but a lack of enforcement by airlines, Health Minister Stephen Donnelly has said.
He was speaking after the booking system was temporarily suspended on Tuesday.
The Department of Health said this was done to allow an assessment of capacity within the system for the coming days.
But speaking on The Hard Shoulder, Minister Donnelly suggested capacity was not the main problem.
"Actually the issue is not the capacity - we have enough rooms to deal with people coming in on the flights where they have verification.
"The problem actually, and it's only for a few days, is that there are a number of airlines which have not been enforcing the legal requirement to not let people board the plane without the pre-flight PCR, the passenger locator form and the verified room."
Asked by host Kieran Cuddihy if airlines were breaking the law, Minister Donnelly said: "They are, yeah - they're breaking NSI on public health grounds.
"I know Minister [Eamon] Ryan has engaged very closely with the carriers".
And he said the availability of rooms is being increased.
"We did anticipate it - and if we weren't dealing with all of these walk-ins from the airlines, we would have enough capacity.
"What we didn't anticipate is the number of walk-ins arriving who have to be accommodated.
"So we're at 654 [capacity] today, on Monday we're moving to about 960, the following Monday we're moving to in excess of 1,300.
"We'll keep that under review, but remember the system is only 19 days old.
"And we started with 33 countries, in less than two weeks we went up from 33 countries to 71 countries.
"But probably even more important, that additional group included very big countries for Ireland: America, Canada, Italy, France - so there was a very big increase in a very short period of time".
Minister Donnelly said an update would be issued "soon", but would not be drawn on a timeframe.
On Ireland set to receive over 500,000 extra Pfizer vaccine doses in coming months, he said this will keep the vaccination plan on track.
"It leaves it, in volume terms, pretty much as we were before all of this happened.
"What we're trying to do is, by the end of June, get four in five adults who want a vaccine their first dose.
"So really the focus for the end of June is the first dose... so for the first dose, the volumes remain the same".