More than 35 staff of the Revenue Commissioners have been investigated for serious misconduct, including theft, fraud and underperformance in the last three years, the Herald has learned.
Documents obtained by this newspaper show the number of serious misconduct cases by Revenue staff has increased year-on-year since 2013.
Revenue management investigated just seven cases of misconduct in 2013, rising to 14 cases in 2014.
The worrying trend continued last year, when 16 cases were investigated.
Documents also show that high-ranking and well-paid workers were among those investigated.
Four higher executive officers - who earn up to €47,379 per year - were subject to inquires, despite regular staff memos on acceptable behaviour at work.
The majority of misconduct cases related to underperformance, breaches of sick leave rules, failing to comply with official procedures, and inappropriate access to data stored by the Revenue Commissioners.
Most of the staff involved in these incidents were dismissed, had their salary reduced or received formal warnings.
However, in other cases staff were sanctioned for other serious issues - including theft, fraud, misuse of the internet, and conflict of interest.
In 2013, a Revenue worker's salary was reduced for misusing the internet, while another worker was dismissed for not obeying civil service codes of practice.
A worker who was being investigated in 2014 for a fraudulent tax refund claim resigned before a sanction could be imposed.
In another case where a worker accessed data inappropriately, they were not dismissed but were demoted and transferred.
Another worker had their salary reduced for theft last year, as did a member of staff who inappropriately accessed data.
Last year, three workers involved in incidents of misconduct either resigned or retired before a sanction was imposed.
Nine cases of misconduct against Revenue workers are still ongoing - including cases of fraud, inappropriate conduct in the workplace, unauthorised removal of property, and the disclosure of data.
Despite the number of misconduct cases increasing, a spokesman for the Revenue Commissioners said the number is "relatively small" compared to the 6,259 staff they employ.
"Allegations of wrongdoing are always fully investigated by the Revenue Commissioners," said the spokesman.
"Where an investigation finds that misconduct has occurred, the official will be subject to disciplinary proceedings under the disciplinary code."
Investigations should take no longer than eight week, but cases can be extended "in the interest of thoroughness".