Almost 600,000 euro of a taxpayer-financed trade union slush fund was spent on foreign travel by Siptu chiefs.
Watchdog the Comptroller and Auditor General (C&AG) found that in 2008, with the economy in freefall, officials spent 199,000 euro on trips and accommodations, and they branded the travel costs inappropriate.
The money was part of a four million euro pot to fund training for public sector workers and union members on social partnership.
One Department of Health employee went on several so-called foreign study trips - paid for out of the fund - to Australia and the US and even trips abroad after he retired in 2005, the investigation has found.
The C&AG uncovered a total of 56 foreign trips paid for, including one to Lanzarote which ultimately had to be refunded.
The Siptu fund administrator told the C&AG that all the trips had fund-related business purposes, but he could not explain what they were.
An investigation by the C&AG found that between 2004 and 2009 598,000 euro was spent on travel and accommodation, 348,000 euro on marketing and promotions and 99,000 euro on hospitality - all of which the audit found were "less clearly within the scope of the funding objectives".
"In some instances, employees of public bodies engaged in foreign travel that was arranged and paid for from the fund," the C&AG report found.
"Such arrangements are inappropriate, because they bypass internal controls over the charging of and accountability for foreign travel expenditure incurred by public employees."
Other inappropriate financial procedures could have been prevented had adequate controls been in place, including 46,000 euro run up - mainly on a credit card - at one restaurant and bar between 2004 and 2009 and 73,000 euro on international flights, also on a credit card, between 2004 and 2009, compared with 7,000 euro on domestic flights.