Capacities at outdoor sporting events will be slashed as part of new government measures designed to tackle the spread of the Omicron variant.
In his latest address to the country, Taoiseach Michéal Martin confirmed that outdoor sporting events must operate at 50 per cent capacity, or a maximum of 5,000.
Matches in rugby's Heineken Champions Cup and the All Ireland Club Championships are to be the most severely effected.
Next month Leinster are scheduled to host Montpellier at the RDS in Pool A of the Champions Cup, with the Sportsground in Galway to host a meeting of Connacht and Leicester.
The following week, Munster are to play Wasps at Thomond Park.
The Taoiseach said the measures will be in place from midnight on Sunday night until January 30.
Sunday's Leinster Club Hurling final between Clough-Ballacolla and Ballyhale Shamrocks at Croke Park will be unaffected.. The same applies to Sunday's Munster Club Football semi-finals at Austin Stack Park and Páirc Uí Rinn.
However, the far side of the new year will see Club Championships feel the crunch.
The festive racing programme will also be severely hit by the new restrictions. The Christmas Festival at Leopardstown is due to get underway on St. Stephen's Day.