Some 400,000 workers have still not received their tax documents for this year and many have been paying too much tax since January 1st, it was revealed in the Dáil yesterday.
It also emerged that an error in the Revenue Commissioners has meant that TDs and the Dáil's own staff have been paying too little or too much tax.
Labour's finance spokeswoman Joan Burton was the first to raise the problem facing people who had not received their tax certificates during a debate on the committee stage of the Finance Bill.
Minister for Finance Brian Cowen acknowledged that certificates of tax allowances and credits still had to be sent to 400,000 people.
Ms Burton said a lot of people had been affected by the delays, and it could impact severely on the finances of people in a variety of circumstances.
She has proposed an amendment to the Finance Bill that would create an office of an advocate for taxpayers allied to the Ombudsman's office.
Later her party leader Pat Rabbitte raised the issue with the Taoiseach and also disclosed that Dáil staff had received a letter warning that there was a problem with their tax certificates.
"Please be aware that an error has been encountered on the new revenue system which has resulted in people both underpaying and overpaying tax.
"Some staff may have been issued with incorrect tax certs as a result of this error which will give incorrect information in relation to their tax credits and cut-off points.
"We would advise all people to check their payslips for any large deviations in their tax credits, cut-off points and net pay."
On a related tax issue, Fine Gael leader Enda Kenny questioned the Taoiseach about why ordinary PAYE taxpayers were not kept better informed about their basic entitlements.
"It is estimated that in respect of medical expenses, bin charges and private rents, over 60 per cent of refunds are not claimed.
"In these three areas alone at least €250 million would be paid back to PAYE workers were these claimed," Mr Kenny said.
A spokesman for the Revenue Commissioners confirmed that as of yesterday morning, 400,000 tax certificates - 20 per cent of the total - had yet to be posted, but said this was not unusual.
An additional 100,000 were posted out yesterday, he said, and everybody should receive their certificates in the post by early next week.
He acknowledged people may have encountered difficulties in contacting the Revenue Commissioners, and said it was the busiest time of year in terms of inquiries from the public.