Dublin Port says all spending on its company credit cards is only ever for business, and is always recorded and approved.
It was reported over the weekend that the state-owned commercial company racked up expenses of more than half a million euro last year.
The Sunday Independent revealed that €5,500 was spent flying Dublin's Lord Mayor, Nial Ring, to Chicago.
The company has also explained that €205,000 spent on a song written for the launch of a new ship included the cost of staging the entire launch event.
As well as commissioning the new music, the money went towards the "staging and rigging for the event, full production, AV and payment to the participating artists and musicians including Lisa Hannigan, Damien Dempsey and John Sheahan".
Other expenses on company credit cards included flights, iTunes subscriptions and food and drinks in Dublin pubs and restaurants.
The Department of Transport has been in contact with Dublin Port, and the Chair of the Oireachtas Transport Committee wants answers.
Dublin Port says it's launched an investigation into the source of the leak, and has reported it to the Data Protection Commissioner.
It describes itself as "well-managed" and "profitable", arguing that "all expenditure listed on credit cards is entirely on company business".
Dublin Port said that total spend on credit cards in 2018 represented 1.2% of a total operating cost base of €43.6m.
"No allegation of wrongdoing has been made in any report.
All expenditure, including travel, subsistence and hospitality is disclosed in the company's financial accounts, which are independently audited and meet all reporting requirements and standards."
Dublin Port has explained that some one-off items were paid for "more efficiently" on company credit cards.
They included things like company iPad cloud storage, an office dishwasher repair charge, and the replacement of a broken coffee pot.