A report by the State's spending watchdog has found that a senior SIPTU official did not seek approval when organising foreign trips.
More than €4m was paid into the SIPTU National Health and Local Authority Levy Fund Account by a range of State bodies in the years 2002 to 2009 - the bulk of which was from the Department of Health.
SIPTU said that it accepts the findings of the Comptroller and Auditor General's report that travel arrangements paid for by the fund were "inappropriate" as they "bypassed internal controls over the charging of - and accountability for foreign travel by public employees".
The inspection found that "there was no effective oversight or formal accountability for the fund’s operations" and that errors could have been prevented had appropriate financial controls been put in place.
These included invoices for expenses totalling €98,000 being submitted twice and cheques being drawn for cash to the value of almost €12,000 without invoices.
Funding totalling €999,000 was returned to State bodies between late 2010 and December 2012.
The Comptroller and Auditor General found that the net cost to taxpayers of the fund’s operations between 2002 and 2011 was therefore around €3.15m.
While records for earlier years are incomplete, it is likely that the Department of Health allocated a further €178,000 for payment to the fund in the years 1998 to 2001 inclusive.
The report found that €2.2m (53% of the public money provided to the fund) was spent on training programmes and grants, and was "consistent with the broad partnership objectives stated by funders".
However, it found that areas such as marketing and promotions (€348,000), travel and accommodation (€598,000) and hospitality (€99,000) are "less clearly within the scope of the funding objectives, and it is not possible to identify the extent of the contribution they may have made to the development of partnership".
The inspection also uncovered other "inappropriate financial procedures". These included no documentary evidence to demonstrate that goods and services which were paid out of public funds were procured in a competitive and fair manner, and payments to some suppliers being made in advance of service delivery.
SIPTUhas asked to appear before the Public Accounts Committee to further clarify its position.