Moderate drinkers have nothing to fear from random breath testing in the morning, Minister for Community and Rural Affairs Éamon Ó Cuív has said.
He believed drivers would have to drink "a lot more" than five pints at night for them to fail a random breath test the following morning.
"To be over the limit the following day, six or seven hours after completing drinking, you'd have to have consumed considerably more alcohol than three or four or five pints.
"I'm not sure how much alcohol you'd have to consume - if you stopped drinking at 12 o'clock, say, before you would still be over the limit at 7am the following morning - but I understand it would be considerably more than the three or four pints that the average rural drinker would have on a quiet night in a pub."
He said he supported random breath testing in the morning and had no sympathy for motorists who get caught.
Publicans have cited morning breath testing as a major contributor to the decline in rural pubs with many drinkers staying at home because they fear being over the limit while driving to work the following morning.
Independent TD Michael Lowry's belief that morning breath testing is a waste of Garda time would appear to have considerable cross-party support.
Of 84 deputies who responded to questions from Newstalk radio station, 34 said such testing is an unnecessary use of Garda resources and should be confined to night-time when drink-drivers are returning home.
The result was described as "unfortunate and disappointing" by the Road Safety Authority's Noel Brett, who said tougher implementation of drink-driving laws, including morning random breath tests, had saved lives.