Pubs, restaurants and hundreds of other businesses are set to remain closed until April.
The hammer blow was issued by Tanaiste Leo Varadkar just hours after Ireland was placed under even more strict lockdown measures.
Mr Varadkar said he was advising the "vast majority" of businesses that they would be closed for the next three months.
"We will review the situation on the 30th of January, and make decisions with regard to the 1st of February", he said.
"But the message I'm giving the business, and the bast majority of businesses, is that if you're open, you'll stay open.
"But if you're closed, it's probably best to plan for the probability that you'll be closed for the first quarter of this year."
Speaking on RTE's News at One with Bryan Dobson, he added: "We're here to help. We'll spend a billion euros every month, in January, February and March if necessary, on the Employment Wage Subsidy Scheme at the current rates, on the weekly CRSS grant at the current rates, and also the Pandemic Unemployment Payment."
The Tanasite said that some businesses may be able to reopen from February if cases begin to drop significantly.
He explained that this would be done in reverse to how things closed, meaning construction would be first in line to return, followed by non-essential retail and so on.
