Former Tánaiste Michael McDowell was "chancing his arm" when he said new media ownership guidelines should be imposed retrospectively, Communications Minister Alex White has said.
The new guidelines, which were published earlier this month by Mr White, would give the minister the power to block proposed media mergers if it is not felt to be in the interest of the public.
The new measures will relate to television, print, radio and online media.
The main factor in any decision will be the size of the operation which those involved already have in the media business.
Former Attorney General and Tánaiste Michael McDowell has written that the new rules should apply retrospectively and relate to existing mergers which the minister feels are not in the public interest.
But speaking on the matter yesterday, the Labour Minister said calls for such a move "beggar belief" as this would go against the Constitution and breach an individual's property rights.
"I think Michael was chancing his arm with that piece and I'll tell you why," he said. "He (Mr McDowell) spoke not just as a former Tánaiste and Attorney General, but as a lawyer for whom I have enormous respect.
"It just beggars belief that anyone would imagine that you could introduce a law that had the kind of retrospective effect that is being contended for in circumstances where we have not just commercial issues ... but a 'hello' written constitution with property rights," Mr White said.
He added that he had never heard "Michael before say that property rights are not sacrosanct until we came to this issue" and said it would not be realistic to force people to divest themselves of assets on foot of a law that was not in place when they acquired the assets.
He said the issue around media mergers differed from a ruling by the British Competition Authority which has ordered Ryanair to sell off its shares in rival airline Aer Lingus.
He said that was a ruling where shares had been "acquired in circumstances where it was unlawful to do so" and so different to media ownership issues.
He concluded that due to property rights which are enshrined in the Constitution, "there is, at the very least, a significant constitutional obstacle involved here and that's why I say Michael was chancing his arm".