Everyone in Kildare, Offaly and Laois is being put under partial lockdown for the next two weeks.
From midnight, people living in the three midlands counties must restrict their travel movements, while pubs and restaurants must also close.
Among the other measures which the Taoiseach will formally announce shortly, all pubs and restaurants in the three counties must close tomorrow, but will be allowed serve takeaway meals.
Shops can still remain open.
The rest of the country will remain in Phase 3.
The decisions being made after the Taoiseach received new advice from the National Public Health Emergency Team on rising cases in the midlands.
The three counties have seen 226 cases in the past 2 weeks, mainly in meat plants.
Those cases accounted for half of all cases in the country in the last fortnight.