The inquiry started last November by the Australian Charities and Not-for-profits Commission into drought relief charities Rural Aid Ltd and Aussie Helpers Ltd is ongoing.
Concerns were raised at that time about their operations and the ACNC sought assurances that the influx of goods and funds being donated was getting to those in need.
A spokeswoman said due to the secrecy provisions in the ACNC Act, they were only able to comment further if certain compliance action was taken again a charity.
This would include issuing a warning or direction, suspending or removing board members, or revoking an organisation's charity status.
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She said the length of an ACNC investigation was determined by a variety of factors, including the complexity of the issue and the charity's willingness to cooperate.
Sixty per cent are completed within six months and 90pc are finalised within a year.
The spokeswoman said the ACNC took all concerns seriously.
"In 2018, the ACNC received more than 1800 concerns about charities, resulting in 16 revocations, 24 compliance agreements and 71 instances of regulatory advice.
"If members of the public have concerns regarding the activities of a charity, we encourage them to raise these by visiting the ACNC website."