Discovery, proportionality and 'tethering to the pleadings'

23 Jul 2026

Cases

Discovery disputes continue to play a critical role in large commercial and administrative law proceedings, particularly where decisions of statutory authorities are challenged on grounds such as improper purpose or Wednesbury unreasonableness.

In Pilbara Ports Authority v Mineral Resources Limited, the Supreme Court of Western Australia provides guidance on the scope of discovery in proceedings reviewing statutory decisions, the importance of proportionality, and the need for discovery categories to remain tethered to the pleadings.

Justice Hill's reasons illustrate the careful balance courts strike between ensuring access to relevant material and preventing discovery from becoming unduly burdensome, especially in complex infrastructure and resources disputes involving historical agreements and significant financial stakes.

Background

The plaintiff, Pilbara Ports Authority (PPA), commenced proceedings against Mineral Resources Limited and Onslow Infraco Pty Ltd seeking payment of invoices issued for a Channel Charge relating to access to the Port of Ashburton LNG shipping channel.

The Channel Charge reflected a pass‑through amount that the PPA was required to pay to Chevron Australia Pty Ltd under various contractual arrangements connected with the development of port infrastructure. Mineral Resources refused to pay the invoices, contending that the charge was not a lawful "port charge" under the Port Authorities Act 1999 (WA).

Mineral Resources challenged the validity of the PPA's determinations made in June and December 2024 and sought extensive discovery from the PPA, including historical executive documents and agreements dating back more than a decade.

Issue

Defendants sought discovery of 10 categories of documents from the Pilbara Ports Authority (PPA) — five are agreed, one partially agreed.

The primary issues on the discovery application were:

Whether the additional categories of documents sought were directly relevant to the issues raised on the pleadings
Whether the proposed discovery was proportionate in light of the nature of the dispute
The extent to which discovery should extend beyond documents formally before the PPA Board, particularly where Wednesbury unreasonableness and improper purpose were alleged
Whether discovery could properly include historic executive and contractual material unrelated to the impugned 2024 decisions

Held

The application for discovery was successful in part.

Justice Hill ordered that the PPA provide discovery of:

The 12 specific "Related Agreements" identified in Schedule 5 of the State Development Agreement;
Board and executive documents from 2024 concerning proposals or decisions to levy the Channel Charge;
Financial documents specific to the Port of Ashburton, rather than consolidated group accounts; and
Any documents on which the PPA intended to rely at trial.

The Court refused discovery of:

Broad categories of historic executive documents dating from 2009 to 2011, on the basis that they were insufficiently connected to the pleaded issues and disproportionate in terms of time, effort and cost.

Interesting Comments Made by the Court

Justice Hill emphasised that: "It is necessary for categories of discovery to be properly 'tethered to the pleadings'."

His Honour also reaffirmed that, while allegations of improper purpose may justify looking beyond formal reasons, discovery will only be ordered where documents bear upon the operative subjective purpose of the actual decision‑maker, in this case, the PPA Board.

Key takeaways

No automatic right to discovery: Discovery is discretionary and must facilitate the timely and cost‑effective resolution of proceedings.
Pleadings are critical: Discovery categories must be closely "tethered" to the pleaded issues and the specific decisions under challenge.
Decision‑maker focus: Where a board is the relevant decision‑maker, discovery will generally be confined to material before (or constructively before) the board.
Wednesbury grounds expand — but do not open — the gates: Allegations of unreasonableness may justify broader discovery, but only within reasonable temporal and factual limits.
Proportionality prevails: Even potentially relevant documents may be excluded where the burden of retrieval outweighs their likely forensic value.

Practical guidance for insurers and their panel firms

For insurers and panel law firms involved in large commercial or public law disputes, the decision provides several practical lessons:

Front‑end pleading discipline matters: Discovery battles will be won or lost by the precision of the pleadings. Vague or expansive allegations invite resistance and judicial pushback.

Temporal limits are critical: Courts are increasingly reluctant to permit "deep history" discovery unless a clear and direct link to the impugned decision can be demonstrated.

Board governance documentation is key: For insured statutory authorities and corporatised entities, well‑structured board papers and decision records can materially narrow discovery exposure.

Early proportionality arguments should be developed: Evidence addressing the burden, cost and difficulty of retrieval (as the PPA did here) can be decisive in resisting overbroad discovery.

Improper purpose claims require focus: Insurers should be alert to the fact that such allegations may justify expanded discovery, but only insofar as they relate to the subjective purpose of the actual decision‑maker.

Conclusion

Even in high‑value disputes involving allegations of improper purpose and Wednesbury unreasonableness, parties must demonstrate a clear and proportionate connection between the documents sought and the pleaded issues.

For statutory authorities, the decision highlights the importance of disciplined decision‑making processes and carefully curated board materials. For challengers, it underscores the need for precision and restraint when framing discovery categories — particularly where historic agreements and long‑running infrastructure projects are involved.