The Campaign Against Household & Water Taxes (CAHWT) has claimed that the 2011 Census and an analysis by a Maynooth academic show that more than 1.8 million households must register for the Household Charge.
The group said that the Government is "spinning" that the number of households eligible for the tax is 1.6 million.
The CAHWT said that NUI Maynooth academic, Rob Kitchin, outlined on RTE radio and in an analysis that there are 1,994,845 dwellings in the State. The analysis said that 18,638 are unsold or exempt, as are 143,000 social housing tenants.
Waivers apply to 53,000 in listed unfinished estates or receiving mortgage interest supplement.
The group said that, however, these also must register, alongside the other 1,755,685 properties liable for the charge.
Gregor Kerr of the CAHWT said: "As of yesterday, the LGMA had 832,000 registrations or awaiting processing. More than 1.8 million must register. This means that almost one million still had not registered for the Household Tax, an amazing figure given both the crude and subtle intimidation.
The Household Charge debacle topped the agenda at this morning's Cabinet meeting, as Government Ministers try to piece together where it all went wrong.
As of Saturday's deadline, just over 805,000 people - or less then half of those liable to pay the €100 tax, had actually paid.
"The media really should carry accurate reporting of the numbers who must register, rather than repeat government efforts to minimise the boycott. There is no more accurate figure of properties than the 2011 Census and no excuse for government misinformation."
Mr Kerr said that, even if the figures increase, there is no way a Government can impose a tax in the long term with such low support in society.
He said: "They should stop calling the handling a 'mistake' - the charge itself is a mistake and should be scrapped."
"The next protest by the Campaign will be at Labour Party conference in Galway on April 14. We brought over 10,000 to Fine Gael's ard fheis, so now we will focus on Labour who pledged not to bring in these household and water taxes before the election."
Questions are now being raised as to what will happen to local authority services, if the €160m collection target is not reached.