Over 15,000 account holders who informed the Revenue commissioners of offshore accounts now have 60 days to regularise their affairs.
Over 7,000 people made contact with the Revenue during working hours yesterday despite the postal dispute.
The Revenue had fixed a midnight deadline last night for account holders to inform them of their intention to make "Notice of Intention to Make a Qualifying Disclosure of an Offshore Tax Default".
Revenue chairman Mr Frank Daly last Friday suggested an upper limit of 10,000 on the number of people likely to notify the tax authorities of their intention to make voluntary disclosures.
People who have filed notification now have 60 days in which to work out how much they owe in tax, interest and penalties and pay the money to the Revenue.
There has been speculation that Revenue could make as much as €1 billion as a result of the offshore accounts' investigation.
Revenue has made €45 million from 1,250 Irish residents who had accounts with one bank's unit in the Isle of Man alone and can now expect millions more before taking non-compliant account holders into account.