Nearly 15,000 off-shore bank accounts are understood to have been made known to the Revenue Commissioners prior to this evening's deadline for avoiding possible prosecution over tax evasion.
Failure to meet the deadline could lead to prosecution and heavy fines and even jail sentences being imposed on top of interest and penalties.
Defaulters could also find their names published in national newspapers, and although voluntary disclosure could lead to a more lenient approach to penalties, interest will still be imposed.
The Commissioners warned that the postal dispute could not be used as an excuse for failing to meet the 5.30 p.m. deadline. Declarations can also be made until midnight by fax to the following Dublin numbers: 6474821, 8277486, 8277780 and 8277782.
Businesses and taxpayers are also reminded that those registered with the Revenue online service can make payments of tax returns due securely. A number of "drop-off" centres are also available during office hours at Dublin, Galway, Dundalk, Navan and Wicklow.
Revenue chairman Mr Frank Daly last week told a Dáil Public Accounts Committee that more than 10,000 accounts could be declared. Account-holders will have 60 days to pay any tax due - including interest and penalties.
Estimates this evening suggest up to 15,000 accounts have been declared.
The Revenue Commissioners began an investigation into offshore accounts last February after contacting ten financial institutions and instructing them to write to customers known to be offshore account holders.
The Minister for Finance, Mr McCreevy, said in November that more than €118 million had been collected from offshore accounts.
Holding the accounts is not illegal but failing to declare taxable income held in them is an offence for someone normally resident in Ireland.