The Minister for Justice, Mr McDowell, has said plans by a midlands judge to sentence all drunk drivers to seven days in jail would be unlawful.
Mr McDowell was speaking in the wake of comments by Judge John Neilan, who says he will put all guilty drivers behind bars for a week while he deliberates over their punishment.
But the Minister said: "It is not possible for a judge in the case of drunk driving to say that part of his procedure will be to remand persons whom he has convicted in custody for a week while considering sentence".
He said: "The law does not permit that, the constitution doesn't permit that. There is a constitutional entitlement to bail.
"The only circumstance in which somebody can be put in custody for a week is for good legal reason and a general policy of the kind outlined by the judge is not a good legal reason," he added.
Judge Neilan announced his new policy at Mullingar District Court yesterday, saying it will take effect in December.
He said the move was necessary to rid Ireland of what he described as "the tragedy" of road deaths and injuries.