Restaurant and Catering SA said it expected 70 per cent of South Australian restaurants would remain closed on Christmas Eve and New Year's Eve because of new part-public holiday penalty rates.
The Association said any venues which opened would have to pay staff 250 per cent penalty rates.
The part-day public holidays were declared this year as part of wider changes to retail trading times for SA.
The penalties apply for staff rostered between 7:00pm-midnight, apart from casuals.
Permanent staff also must be given the option of choosing not to work at those times.
Association CEO Sally Neville said most venues could not afford to open.
"It's going to be quite a challenge for restaurants over this period.
The large majority have contacted me to advise me they will be closed during the period," she said.
"Some will open, the businesses that are open will be applying a surcharge to their customers." Meanwhile, the Rundle Mall Management Authority said the number of visitors to the shopping precinct over December was up about 5 per cent on last year.
CEO Ian Darbyshire said it was still too soon to know whether the extra visitors meant increased profits.
"We don't have those final figures out until January when we do some research on it, but there's definitely more people in the mall and the word on the street from the retailers is they're starting to spend," he said.