Revenue says it won't impose any surcharge on income tax returns filed online this week due to a problem with its web system, ROS.
Yesterday, Revenue extended the 'pay and file' deadline until 6pm this evening due to technical problems with its website.
However, the online service had to be taken offline for a period earlier today in an effort to "fully resolve the issues".
They said the system was expected to be up and running again from around 1pm.
In a statement, Revenue said: "Revenue acknowledges the difficulties and frustration being experienced by taxpayers and agents who are continuing to try and file returns today and apologises for the inconvenience.
"In light of the difficulties experienced with the ROS system over the last couple of days, a surcharge will not apply to any returns filed this week."
Revenue previously said up to 4,000 returns were filed per hour throughout Tuesday morning.
The volumes caused intermittent downtime for some of those using the online system.
While it was still possible to file returns, Revenue said the volume of submissions were less than expected - prompting a decision to fully refresh the system.