Tens of thousands of people planning to travel to Ireland over the coming weeks will have to ensure they have a negative Covid-19 test before they leave their country of origin.
The move will cause significant angst for people planning visits home to see family and those jetting off for short breaks over the festive period.
The new rules could see fully vaccinated passengers stranded in countries they travelled to if they cannot produce a negative Covid-19 test before returning home.
Depending on local rules, passengers could be forced to extend their stays abroad for up to 10 days if they get a positive test result.
Negative test results will be required from passengers arriving from all countries, including Britain. However, vaccinated people travelling from Ireland to Britain will not be required to produce proof of a negative test. Passengers will also be able to fly from Britain to Belfast without having to show a negative test result.
The Cabinet agreed to review the restrictions after two weeks, but a senior Government source said they expect the rules to be place all the way up to Christmas.
"I can't see us learning enough about Omicron that would reassure us in two or three weeks," they said.
There are concerns the new variant is already in Ireland with Government sources saying the National Public Health Emergency Team (Nphet) is examining a number of cases from October which may be the Omicron variant.
The Cabinet was briefed on positive indicators on the spread of the virus but was warned that Nphet is likely to recommend more restrictions when it meets tomorrow.
The travel restrictions announced yesterday are amongst the strictest in Europe, with only Portugal introducing a similar regime. Nphet wanted incoming passengers to be required to produce a negative PCR test taken within the 72 hours before they arrive in Ireland.
However, the Government instead decided to also permit passengers to produce a negative antigen test taken within the 48 hours before their arrival.
Antigen tests must be administered professionally and cannot be home test kits.
Passengers will also have to show their Covid Digital Certificates on arrival in Ireland.
Passengers coming into the country who refuse to produce a negative test may face fines, a government spokesperson said. Some may even face imprisonment as a last resort if they refuse to comply with the new international travel rules.
The Government is also examining possible fines for carriers that do not conduct proper pre-flight checks of passengers to ensure they have their test results.
Upon arrival in Ireland, there will be "spot checks" by border management units and immigration gardaí. Passengers without a test result or without the correct test will have to quarantine at home and immediately get a PCR test.
Officials were last night drafting new legislation to underpin the travel restrictions for passengers.
Separately, the Government urged parents with children under the age of 12 to reduce indoor socialising over the coming two weeks.
Nphet recommended that children under 12 should avoid indoor settings.