Pubs, restaurants and cafes are banned from serving alcohol from Friday evening and must close at 18:00 GMT, other than for takeaway service.
Businesses said it was "a devastating hammer blow" after going to lengths to keep customers safe.
They said the restrictions will also significantly impact the supply chain.
At the Glamorgan Brewery in Llantrisant, Rhondda Cynon Taf, staff have been pouring barrels of beer down the drain because it now cannot be sold in pubs.
On Thursday, 58 of the company's 64 employees went back onto furlough.
Director David Atkins said the new measures are "an absolute kick in the teeth".
"This time last year we probably turned over about £1.5m for the month of December. This year, it's £50,000.
He added the majority of their beer - about 45,000 pints - will have to be thrown away.
At The Cricketers pub in Pontcanna, Cardiff, staff were also pouring away beer on Friday afternoon.
Simon Buckley, of Evan Evans Brewery which supplies the pub said: "How can it be right and safe to open to serve food in pubs but not alcohol? It defies logic.
"Why is 6pm the bewitching hour as opposed to 10pm? In these difficult times - and the month of December particularly - the lost revenue is significant."
James Cunningham, manager of the Ruthin Castle Hotel in Ruthin, Denbighshire, said customers have appreciated the safety measures put in place and the new rules were "incredibly frustrating".
"Whenever they can, people want to try to come out and enjoy themselves in these very, very testing times," he said.
He described the measures as a "devastating hammer blow" to the hospitality industry.
"Figures show that less than 5% of all settings of infection happen in hospitality - and yet here we are once again taking the hammer blow," he said.
"There's no guarantee those restrictions are going to be lifted," he said.
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