Local Authorities have raised nearly €15m from people obliged to pay a €200 charge for owning a second property.
The official deadline for payment is tomorrow, however property owners have another month to pay the charge before penalties kick-in.
Chairman of the County and City Managers' Association Eddie Sheehy warned that people who are liable need to pay now, or incur penalties of €20 per month, and risk prosecution.
He said 85% of payments have been made online.
The Government had anticipated that the charge would result in €40m being raised by Local Authorities.
A Department of Environment spokesman said the slow start had been expected, and expressed confidence the €40m figure would be reached by the end of October.