The Department of Housing says the Minister has no discretion when it comes to what areas of the country are rent pressure zones.
Officials are before an Oireachtas committee over why certain parts of the country have a rental cap, while others do not.
They say that mathematical formulas and data from independent agencies are used in calculations.
Assistant secretary, Bairbre Nic Aongusa says the Minister can't intervene.
"The process is independent. It's independent of the Minister in the sense that the Minister has no discretion in terms of deciding whether an area is in or out of a rent pressure zone," she said.
"The process is set down very clearly. The housing agency has to consult with the local authority concerned, but the housing agency then makes its independent judgement as to what area is put forward."