The Restaurants Association of Ireland (RAI) has said no-shows continue to be "soul-destroying" for the hospitality sector.
The industry body said one Dublin City centre restaurant had 18 people book and confirm a table yesterday, only to never arrive.
Friday saw the return of inboor bookings after businesses were restricted to takeaway service and prior to that outdoor dining.
The easing of new Covid-19 restrictions to allow the hospitality sector to operate over the festive period were introduced this week as part of the government's Level 3 adjusted plan for Christmas.
RAI Chief Executive Adrian Cummins said restaurant owners can not afford to keep tables empty after struggling so long with the impact of Covid-19.
"Diners are booking restaurants and not turning up which is soul-destroying for these businesses who are economically flattened at the moment trying to save their businesses.
"Every customer that books a seat that doesn't show up is effectively lost revenue and money gone from that business at a time when they need every customer they can get to keep their businesses afloat," said Mr Cummins.
In a sign of the pressure the industry is under, one Cork restaurant yesterday published an appeal on social media for available bookings after two reservations for tonight cancelled.
Would really appreciate the share. Devastated, 2 tables of six cancelled for tomorrow night. So we have availability at 8.30 for 6 and 8.45 for 6. Thank you 🙏— Dockland (@docklandcork) December 4, 2020
Dockland, run by restaurateur Beth Haughton, said two tables for six had cancelled yesterday evening and that the effect of this was "devastating."
We now have both tables rebooked. The power of Twitter and kindness. Thank you so much 😊 #thankyou— Dockland (@docklandcork) December 5, 2020
Happily, though the appeal was successful for the restaurant and both tables were filled.