The rule applies whether guests are hotel residents or not.
A new Covid restriction forcing bars, nightclubs, and restaurants to close at midnight is set to come into effect from tonight, Thursday 18 November.
The Irish Hotels Federation has stated that the Government confirmed the new closing time applies to hotel bars and all events that take place in hotels - including weddings.
The closing time applies whether attendees are hotel residents or not.
In a statement, its said:
"Due to the current prevalence of the coronavirus in the community, we are hearing from our members that businesses are adopting a cautious approach in relation to hosting business events and meetings."
It emphasised that public health is its number one priority.
Taoiseach Michael Martin announced the new Covid restrictions on Tuesday, which also included the reintroduction of working from home and stricter guidelines regarding household close contacts.
He has since stated that the coming weeks remain uncertain and further restrictions
cannot be ruled out. He said the latest NPHET projections are extremely worrying.
On Wednesday, Chief Medical Officer Dr. Tony Holohan said up to
400,000 people could contract Covid before Christmas if behaviour is not changed.
He also said that employers should reconsider staff Christmas parties and called for "collective adherence" to regulations.
"An organisaton should look at itself and the kind of measures it needs to take, we are advising people to stay at home as much as possible and work from home, those are responsible decisions.
“What we are trying to prevent is potentially 200,000 or even double that picking up this infection in the month of December.
"So we would see 200,000 people being asked to self-isolate over the Christmas period where they can’t meet up with friends, family or anybody else.
"These are huge impacts that will be placed on the population at this time of the year if we don't find it within ourselves to improve our collective adherence.
"None of those people are infected yet, if we have 200,000 people infected 4,000 will end up in hospital at Christmas."
3,633 new cases of the virus were confirmed on Wednesday evening.
As of Thursday, the number of patients with Covid in hospitals is 643. Of them, 118 people are in intensive care units.
