The National Anti-Corruption Commission (NACC) informed Tourism Australia it would not launch an investigation into an expenses scandal, just hours after its chief executive refused to answer questions about the matter in parliament.

Last week, Tourism Australia CEO Phillipa Harrison revealed she had referred three former staff to the NACC after they were sacked for charging taxpayers for personal travel.

Appearing before Senate estimates, Ms Harrison said the three staff had repaid $137,441 after the incident came to light.

But she insisted could not provide parliament with further details of the incident — including the names of those involved — because that could prejudice a future probe from the NACC, and the commission had provided her with advice to show restraint in her public comments.

The anti-corruption watchdog said it informed Tourism Australia the day after Ms Harrison's evidence to the Senate that it would not wade in.

"The commission can confirm that it has recently decided to take no further action in relation to the referral, on the basis that, prior to the referral, the matter had already been fully investigated, the employees terminated and the funds repaid, so there was nothing that the commission could now usefully add to the process," the NACC told the ABC.

The incident had caused some consternation in the Senate, with the demands for secrecy from the NACC as it considered the referral seen as interfering with the work of parliamentarians scrutinising Tourism Australia's operations.

"I have to say, this is the first time in my experience where a direction from the NACC has directed an official not to make a public statement," Trade and Tourism Minister Don Farrell told the Senate committee last week.

"This does present some significant issues which I myself would like to get clarified."

The ABC has approached Tourism Australia and Senator Farrell for comment.

The federal opposition argued it was now incumbent on the government to come clean with details of the incident.

"The minister was made aware that taxpayer dollars had been fraudulently spent by public servants in late 2023," Shadow Trade and Tourism Minister Kevin Hogan said in a statement.

"There is now no anti-corruption investigation to hide behind.

"We need details about the embezzlement and how it has been handled."

Mr Hogan asked whether the matter would be referred to the Australian Federal Police as a result of the NACC refusing to weigh in.