Opposition immigration spokesman Scott Morrison says he has been "totally transparent" about the fact a major logistics company funded his visit to Nauru.
Mr Morrison visited the tiny Pacific nation this week and announced coalition plans to build a new 2000-bed processing facility for asylum seeker boat arrivals.
His flight was paid for by Toll Group, leading to government claims of a conflict of interest.
Toll has been working on multi-million dollar contracts to upgrade Australia's Nauru processing centre since late 2012.
Mr Morrison says he declared Toll's role on his parliamentary register of interests.
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"We're not in the middle of any tender process. We're in opposition, we're not in government, and Toll Holdings were going up there for the ordinary course of business anyway, which was in my disclosure," Mr Morrison told ABC radio on Wednesday.
"It is not the first time we've had privately funded trips to Nauru.
"We were there with Tony Abbott a year or so ago. ABC and Fairfax and all other journalists were on that trip as well. This is a fairly standard way of doing things when you're in opposition."
Mr Morrison was accompanied on his trip by News Corp Australia reporters.
He hit back at reports in Fairfax newspapers that the flight had been chartered for the coalition, saying "the plane was going there anyway".
"That was a misreport by Fairfax yesterday, whom I just assume had a bit of sour grapes that they weren't there as well," Mr Morrison said.
Deputy Prime Minister Anthony Albanese on Tuesday said it "extraordinary" that Toll had paid for Mr Morrison's trip.
Prime Minister Kevin Rudd said Opposition Leader Tony Abbott had questions to answer about Mr Morrison's trip.
"I think it's time for Mr Abbott to fully account for what has occurred," Mr Rudd told reporters in Sydney.
"Was Mr Abbott aware of all of this? What actually transpired?"
