Motorists below the drink-drive limit in Northern Ireland could find themselves breaking the law simply by crossing the border this week.
Drivers in the Republic face new lower drink-drive limits from midnight on Thursday.
The new Irish breath test limit of 50mg of alcohol per 100 millilitres of blood - down from the current 80mg - is the equivalent of drinking less than one pint of beer.
However, the current drink-driving limit in Northern Ireland remains 80mg of alcohol per 100ml of blood. In a bid to reduce the number of deaths related to drink-driving here, Stormont Environment Minister Alex Attwood recently announced that he intends to reduce the limit to 50mg.
Meantime, any motorists under the legal limit in Northern Ireland but caught just over the new drink-driving limit in the Republic will be hit with penalty points and a €200 (£170) on-the-spot fine instead of losing their licence.
There will also be a virtual 'zero-tolerance' limit of 20mg for learner and professional drivers in the South.