A €100 fine for anyone crossing the border into the Republic from the North is in effect.
The new measures apply to anyone who is not a resident in the Republic of Ireland.
Every adult in the car will be fined and not just the driver.
People given a Covid-19 related fine have 28 days to pay.
Over 3,500 people were fined in the Republic for non-essential travel, according to figures up to the end of last week.
