More than 5,000 suspected tax evaders are to get letters in the post warning them the Revenue Commissioners are investigating their affairs.
It is the second stage of the investigation into insurance policies used by people to hide hot, or untaxed, money from the Revenue.
Investigators have already netted €422 million from the first 5,000 cases as they check up on people who took out single premium insurance policies.
Another 5,000 cases are now being looked at.
A spokesman for the Revenue said people who hid money in these schemes could expect a letter in the post in the coming days.
"We will be issuing 5,000 inquiry letters in connection with this investigation within the next few days," he said. Investors are believed to have paid lump sums of untaxed money into insurance schemes, allowing the policy to mature over a few years before removing it by paying a relatively small fee.
The money then appeared legitimate and taxed.
This is just one of seven special investigations the Revenue Commissioners have carried out over the last few years. Up to the end of February this year, they have recovered just shy of €2.3 billion from 31,950 taxpayers as a result.