Implied waiver of legal professional privilege: Key lessons from Mastercard v ACCC

The Full Federal Court’s recent decision in Mastercard Asia/Pacific (Australia) Pty Ltd v Australian Competition and Consumer Commission [2026] FCAFC 37 (Mastercard v ACCC) provides updated guidance on when an implied waiver of legal professional privilege can occur and its effect. It demonstrates that a waiver may arise where a party’s conduct is inconsistent with maintaining confidentiality, even if the party has not expressly disclosed the content of privileged communications.

The decision is an important reminder for litigants and practitioners, particularly those who work on regulatory matters, to be cognisant of the information disclosed in affidavits, discovery and other evidence.

Implied waiver of legal professional privilege

Legal professional privilege protects confidential communications and, in some cases, confidential documents made for the dominant purpose of obtaining legal advice or legal services. Privilege may be waived expressly or impliedly where the privilege holder acts in a way that is inconsistent with maintaining the confidentiality that privilege is designed to protect.

The dispute in Mastercard v ACCC

The Australian Competition and Consumer Commission (ACCC) commenced civil penalty proceedings against Mastercard Asia/Pacific Pte Ltd and Mastercard Asia/Pacific (Australia) Pty Ltd (together, Mastercard), alleging that it engaged in anti-competitive conduct in connection with the supply of credit card acceptance services by encouraging merchants to sign up to strategic merchant agreements (SMAs). The ACCC claimed that these SMAs would discourage merchants from routing transactions through EFTPOS, Mastercard’s main competitor.

The central issue before the Full Court was whether Mastercard had impliedly waived legal professional privilege over certain communications after filing two affidavits made by its senior executives, Mr Koh (Vice President, Finance, Mastercard Singapore) and Mr Molu (former Chief Financial Officer, Mastercard Singapore). The affidavits referred to the considerations Mastercard had taken into account when proposing the SMAs to merchants, and stated that the company had not considered an anti-competitive purpose in doing so, but instead had legitimate commercial purposes for encouraging merchants to sign up.

The primary judge found that the affidavits made several implied assertions about the contents of communications between Mr Koh and Mr Molu and other Mastercard employees, including in-house counsel. In the primary judge’s views, those references put the subject matter of those communications in issue, such that there had been an implied waiver of privilege.

In broad terms, Mastercard contended that the primary judge erred in finding that:

• particular paragraphs of the affidavit gave rise to an implied waiver
• the waiver operated upon filing the affidavits with the Court (that is, before the affidavits were read or relied upon in open court).

On 30 March 2026, the Full Court dismissed Mastercard’s appeal and held that, in making assertions about the purpose of the SMAs in the affidavits, Mastercard had opened up communications regarding the purpose of the SMAs to examination.

Additionally, the Court held that waiver of certain privileged communications between Mr Molu and Mr Koh and others at Mastercard arose because the contents of their affidavit evidence advanced a position on a topic central to the controversy (being the purpose, strategy and likely effect of the SMAs), which was inconsistent with Mastercard also maintaining privilege over these communications between them and others at the company which discussed the topic. The waiver was limited in its scope to communications between particular dates which Mr Koh and Mr Molu were a party to that recorded or referred to a strategy, purpose and, in the case of Mr Molu, the likely effect of the SMAs.

Finally, the Court also held that the waiver occurred when those affidavits were filed, rather than read in court.

Key takeaways and considerations for litigants

The main practical lesson from Mastercard v ACCC is that if a party puts forward evidence or submissions about the purpose, strategy or rationale for conduct in issue in proceedings, it may be required (in fairness) to disclose otherwise privileged communications that relate to the same subject matter. The risk is particularly acute where the evidence is served and filed as evidence-in-chief on behalf of that party.

Litigants should therefore manage their evidence carefully, particularly where affidavit evidence risks placing the substance of legal advice, or the existence and role of advice, in issue.

For litigants and their lawyers, the key takeaways and findings include:

• implied waiver can arise without disclosing advice: Implied waiver may occur even where a party does not explicitly refer to legal advice. The question is fact based and turns on whether the party’s conduct (including affidavit evidence) is inconsistent with maintaining confidentiality over communications on the same subject matter
• beware of ‘partial’ or ‘selective’ disclosure by topic: Evidence that advances a party’s case on the purpose or strategy for conduct in issue may require disclosure (to avoid unfairness) of privileged communications dealing with the same topic. Lawyers should avoid including unnecessary narratives in affidavits about motivations, legal review processes, or reasons for decisions made
• regulator-facing narratives can have privilege consequences: Where a dispute involves a regulator, internal explanations of purpose and strategy often intersect with legal advice. Litigators should ensure that affidavit evidence, correspondence and submissions present a consistent account that does not unnecessarily put legal advice, or advice-dependent reasoning, in issue
• document control during investigations: Where regulators are conducting investigations, document management is critical. Litigants must ensure that privileged documents are clearly identified and protected, particularly where they relate to the subject matter of the dispute. This can include by maintaining clean privilege logs and controlling the circulation of advice. The decision also underscores that waiver can be found to arise on the filing or service of affidavit evidence, so any privilege review should occur well before those steps are taken
• align procedure with strategy: Pre-trial steps, including the preparation, service and filing of affidavits, can create waiver risk. Lawyers should review for privilege when drafting affidavits, consider whether evidence can be framed at a higher level of abstraction, and test whether any assertion that needs to be made would be said to ‘open up’ communications on the same subject matter. As highlighted above, the filing of an affidavit at the pre-trial stage was sufficient to trigger the waiver of privilege under the principle of inconsistency, therefore litigants must carefully consider the implications of procedural steps on their overall litigation strategy.

These takeaways are particularly relevant for corporations involved in regulatory investigations. They serve as a reminder of the importance of maintaining consistency in legal and commercial communications and highlight the risks of subject-matter waiver where affidavits or other communications advance a narrative about purpose or strategy.

If you have any questions about implied waiver of legal professional privilege or need assistance with preparing evidence or responding to a regulatory investigation, please contact us here.

Disclaimer
The information in this article is of a general nature and is not intended to address the circumstances of any particular individual or entity. Although we endeavour to provide accurate and timely information, we do not guarantee that the information in this article is accurate at the date it is received or that it will continue to be accurate in the future.

Published by:

Alana Giles

Katerina Stevenson

Alexandra Cowden, Leah Sandow

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