Affidavits can cost you privilege. On 30 March 2026, in Mastercard v ACCC, the Full Court confirmed that asserting what was (or wasn’t) said internally may waive legal professional privilege – even before trial. Litigants must align evidence strategy with privilege risk or face forced disclosure of sensitive communications.
Case Summary
Mastercard v ACCC: When Affidavit Evidence Triggers Waiver of Privilege
The Full Federal Court’s decision in Mastercard Asia/Pacific (Australia) Pty Ltd v Australian Competition and Consumer Commission [2026] FCAFC 37 is a significant development in the law of implied waiver of legal professional privilege, with important consequences for how parties prepare affidavit evidence in complex litigation.
At its core, the decision confirms that privilege may be lost not only by disclosing legal advice, but by advancing a positive factual narrative while withholding related communications—and that this can occur well before trial.
Background to the Proceedings
The ACCC has commenced civil penalty proceedings against Mastercard alleging contraventions of ss 45, 46 and 47 of the Competition and Consumer Act 2010 (Cth).
The regulator alleges that, from 2017, Mastercard implemented a “credit leverage strategy” through strategic merchant agreements (SMAs). According to the ACCC, the purpose and effect of that strategy was to discourage merchants from routing debit transactions through the Eftpos network, thereby substantially lessening competition in the market for debit card acceptance services.
Mastercard denied any anti-competitive purpose. It pleaded that the SMAs were driven by legitimate commercial objectives, including:
- competing with rival payment schemes;
- responding to merchant expectations; and
- increasing Mastercard transaction volumes.
The Evidence and the Privilege Dispute
To support its defence, Mastercard relied on affidavit evidence from two senior executives, Mr Koh and Mr Molu, both of whom had been involved in reviewing or approving SMAs.
Their evidence went beyond merely denying the ACCC’s allegations. In substance, they asserted that:
- preventing Eftpos from competing was not their purpose or understanding;
- no one had communicated such a strategy to them; and
- their understanding was that the SMAs were commercially legitimate and pro-competitive.
The ACCC argued that, by advancing that evidence, Mastercard had impliedly waived legal professional privilege over communications involving those witnesses that related to:
- the strategy underpinning the SMAs;
- their purpose; and
- their likely competitive effect.
The primary judge accepted that submission in part and ordered Mastercard to produce defined categories of documents. Mastercard appealed that decision to the Full Court.
Key Issues on Appeal
The appeal raised three central questions:
- Is implied waiver confined to cases involving disclosure (express or implied) of legal advice?
- Did the affidavits of Mr Koh and Mr Molu give rise to waiver in this case?
- Can waiver arise before affidavit evidence is formally read at trial?
The Full Court’s ReasoningWaiver is governed by inconsistency—not rigid categories
The Court reaffirmed the principle in Mann v Carnell:
the touchstone of implied waiver is whether the privilege holder has engaged in conduct inconsistent with maintaining the confidentiality that privilege protects.
Importantly, the Court rejected Mastercard’s argument that waiver is limited to situations involving disclosure of the content of legal advice. While such cases are common, they are not exhaustive.
The Court emphasised:
- mere relevance is not enough to establish waiver;
- putting state of mind in issue is not, by itself, sufficient; but
- waiver may arise where a party makes positive assertions on a topic while withholding communications on that same topic.
The affidavits went beyond mere denials
The Full Court held that the evidence of Mr Koh and Mr Molu was not limited to putting the ACCC to proof. Instead, it advanced a positive factual narrative about Mastercard’s internal strategy and understanding.
By asserting:
- what was not communicated internally;
- what did not form part of their thinking; and
- what the purpose of the SMAs was,
Mastercard effectively invited scrutiny of the contemporaneous communications that informed (or may have contradicted) those assertions.
In those circumstances, it was inconsistent to maintain privilege over communications involving those witnesses on the same subject matter.
Waiver can arise pre-trial
The Court also rejected Mastercard’s argument that waiver could only arise once the affidavits were read into evidence at trial.
It held that:
- the filing and service of affidavits pursuant to case management orders is a significant forensic step;
- in the context of modern litigation and the overarching purpose in ss 37M and 37N of the Federal Court of Australia Act 1976 (Cth),
waiver can properly be determined before trial; and - delaying the issue could create unfair forensic advantages and undermine efficient case management.
Scope of the Waiver
The Court endorsed a confined, subject-matter approach to waiver.
The production orders were limited to communications:
- involving Mr Koh or Mr Molu;
- within the relevant time period; and
- concerning the strategy, purpose, and (for Mr Molu) the likely effect of the SMAs.
This reflects the Court’s balancing exercise—ensuring fairness without extending waiver beyond what is necessary.
Why This Decision Matters
This case carries significant practical implications for litigants and their advisers:
Affidavit evidence is a privilege risk
Carefully worded but assertive statements—such as:
- “no one communicated that strategy to me”;
- “that was not our intention”; or
- “my understanding was that the purpose was legitimate”
may trigger waiver if related communications exist.
Privilege and evidence strategy must be integrated
Privilege cannot be managed solely at the document review stage. Before serving affidavit evidence on contested issues, parties must consider whether privileged communications:
- inform,
- qualify, or
- contradict
the proposed evidence.
Waiver can occur early in proceedings
The decision confirms that privilege disputes may crystallise before trial, shaping discovery obligations and litigation strategy from an early stage.
Key Takeaways
- Implied waiver turns on inconsistency, not fixed categories.
- Disclosure of legal advice is not required for waiver to arise.
- Positive affidavit evidence on purpose, strategy or understanding may open the door to privileged communications.
- Waiver can arise upon filing and serving affidavits, not just at trial.
- Courts will confine waiver by subject matter, but will not permit selective disclosure that creates forensic unfairness.
Outcome
The Full Court dismissed Mastercard’s appeal and ordered it to pay the ACCC’s costs.5
