The Acts Interpretation Act doesn't give decision-makers an automatic right to revisit a decision.
Decision-makers who want to revisit a decision, and potentially remake it, often assume they have the power to do so, even if the relevant Act does not spell this out. That assumption could be seriously flawed, following the Federal Court's decision in MJD Foundation Limited v Minister of Indigenous Affairs  FCA 1172.
A decision-maker's power and the Acts Interpretation Act
Section 33(1) of the Acts Interpretation Act 1901 says:
"Where an Act confers a power or function or imposes a duty, then the power may be exercised and the function or duty must be performed from time to time as occasion requires."
This has been used by decision-makers to allow them to revisit, revoke or vary an existing decision.
The decision(s) in the MJD Foundation case
The MJD Foundation made an application for funding from the Aboriginals Benefit Account; the Minister for Indigenous Affairs approved $10m funding from the account under the Aboriginal Land Rights (Northern Territory) Act 1976 (Cth).
Following the change of government in 2013, the new Minister decided to revoke the decision to approve the funding, relying upon section 33(1).
Justice Flick confirmed that determining whether a discretionary power can be exercised from time to time, or will be spent once it is exercised, will depend on the interpretation of the statute bestowing the relevant power.
However, under the Land Rights Act, once the Minister directed an amount be debited, the Minister could not direct that an amount not be debited. The Minister could use the power to direct that further amounts be debited, but could not revisit an existing direction to revoke or vary that direction. In other words, the power conferred could only be exercised once, and not from time to time (the exception being where the Minister made a direction that was a legal nullity). Given that statutory framework, the Minister could not rely on section 33(1) of the Acts Interpretation Act to revisit, revoke or vary an existing direction.
The take-home message here is that whether a particular statutory power can validly be revisited once it is exercised will depend on the particular statutory context. Decision-makers should not assume that section 33 of the Acts Interpretation Act will permit a decision to be re-made.