Almost a fifth of homeowners eligible to pay the controversial property tax have yet to register on the day of the deadline.
They have just over 12 hours to file a return to Revenue, outlining how they intend to pay the tax, which comes into force on July 1.
Homeowners who miss the midnight deadline have been warned they could have the tax directly deducted from their salaries or pensions.
A Revenue spokesman confirmed 1.35 million people had filed their returns by midnight on Monday, leaving around 310,000 yet to register.
The tax authority sent 1.66 million letters to property owners all over the country.
Left-wing TDs have continued to campaign against the tax, insisting the hard-pressed public has been stretched enough by the Government’s spending cuts and tax hikes over the last two years.
The rate was set at 0.18% of the property value, rising to 0.25% for homes worth more than €1m.
This will see the owner of a home worth the national average price of €157,400 paying nearly €300 every year.
People are required to self-assess the value of the property, but Revenue has provided estimates based on the average value of homes in particular areas.
The annual sum will be collected by the Revenue Commissioners.
Waivers will apply to homeowners earning less than €15,000, those living in ghost estates and properties with pyrite damage.
The Revenue helpline, 1890 200 255, will be open for registrations until midnight.
Homeowners will also be able to register online at revenue.ie before the deadline.