Defence Minister Richard Marles revealed his interactions with a number of US officials after returning from Washington DC earlier in the week.
While he mentioned meeting with Vice President JD Vance, Secretary of State Marco Rubio and White House Deputy Chief of Staff Stephen Miller, Mr Marles also mentioned it was fantastic to "see" Defence Secretary Pete Hegseth on Tuesday local time.
But on Thursday, a Pentagon official revealed to Nine that there was no formal meeting between the defence minister and his US counterpart, instead describing their face-to-face as a "happenstance encounter".
Treasurer Jim Chalmers said he had not yet been debriefed on any discussions with Mr Hegseth but assured his colleague had secured "very senior meetings."
"I find it quite strange, frankly, to see some of this kind of kick back," he told reporters in Canberra.
"Richard, as always, is engaging with American counterparts enthusiastically, diligently, professionally."
Opposition senator Bridget McKenzie said it appeared Mr Marles wasn't able to have "deep engagement" with a person important to the US-Australia relationship.
But coalition finance spokesman James Paterson acknowledged Mr Marles previously had "extensive dealings" with his US counterpart.
"It's a good thing that the deputy prime minister has been to Washington DC, has met with the vice president, has met with Secretary of State Rubio." he told Sky News.
"That's the kind of relationship we aspire to have and want to have with the United States."
Mr Marles held a meeting with the defence secretary in June where Mr Hegseth said Australia should lift its defence spending to 3.5 per cent of gross domestic product.
US demands have taken the spotlight in recent months after the Pentagon launched a review into the trilateral AUKUS pact, creating doubt over the future of Australia's nuclear submarines.
The threat of US tariffs has already taken a toll on the postal system after President Donald Trump unveiled a 10 per cent tariff on most Australian goods sent to America.
Australia Post announced on Tuesday it would halt services to the United States, introducing a temporary ban on items worth more than $A150.
The tariffs are expected to affect about 3000 small businesses in Australia and Trade Minister Don Farrell said he has already raised the issue with the general counsel of the United States Trade Representative Jennifer Thornton.
"We've said to the Americans, 'firstly, we don't agree with what you've done, but if you're going to do it, then you've got to do it in a way that people can comply," Senator Farrell told reporters.
AAP has reached out to Mr Marles' office and the US Department of Defence for comment.
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