The Government has been accused of imposing a 'curfew' on restaurants by telling them to close by 11pm.
The Restaurants Association of Ireland (RAI) says yesterday's announcement came as a "total shock" to the sector.
They're also suggesting the move will "fuel house parties right across the country".
According to the Government, restaurants and pubs operating as restaurants will be required to close by 11pm other than for take-out and delivery services.
Speaking on Lunchtime Live, Adrian Cummins - CEO of the RAI - said restaurant owners are "perplexed, annoyed and in shock" today following the announcement.
He said: "It is a curfew. What'll happen here - and every customer that's coming in today is telling our members - this is going to fuel house parties right across the country, especially at the weekends.
"If you are asking restaurant owners to clear the premises and get people out on the streets at 11pm... what's going to happen then?
"They'll all jump into taxis and head to the homes of whoever has a house party for the next hour and a half."
Mr Cummins also questioned whether new legislation will be needed to enforce the new rules.
He said: "You are now looking at changing the licencing laws in the country, and I think they may not have thought this through and may be on sticky ground. I don't know yet, but I'd like to see a Minister or someone to say that."
The RAI has already started lobbying against the latest move, suggesting the loss of income may make some businesses unviable.
Mr Cummins argued that the extra hour - even if as late as 11pm-12am - is the difference between "viability and businesses closing" for some restaurants.
He's also now calling for NPHET to coordinate more closely with business groups.
He suggested: "NPHET have a job to do, and they have to take the best advice from a medical perspective.
"But they should also have a business voice on NPHET to flag these issues in advance, before we communicate to the public so that it is talked through."