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.