The Australian Taxation Office (ATO) has held back 200,000 tax assessments as it investigates data integrity concerns with its newly implemented IT system.
Previously, it expected to have processed "the majority" of tax returns that had been backlogged by the implementation process by the end of last week.
On Monday, however, Second Commissioner David Butler reported "some minor problems which have delayed us issuing some of those remaining stockpiled refunds and assessments while we ensure the integrity of our data".
The issue arose from the incompatibility of certain data formats with different components of the ATO's new integrated core processing system (ICP).
Affected assessments included those that involved: a baby bonus; entrepreneur tax offset; primary production averaging; exempt foreign employment income; special professional averaging; eligible termination payments; superannuation lump sum payments; and non-resident withholding tax.
No data was expected to have been compromised.
The ATO said it resumed processing the stockpiled refunds and assessments on Tuesday.
"In some situations the format of data under the new system did not interact as well as we had expected with some other systems," Butler told iTnews.
"To fix this, we had to slightly amend the format of our data so that it could interact with the other systems.
"We had to run tests on potential fixes to ensure there would be no unintended or unexpected results which could potentially compromise any data.
"We remain committed to ensure the reliability of our processes even if this slows us down."