Joinder of Additional Parties in SIAC Arbitration: Rules, Procedure, and Key Considerations

2. Reasons for Parties to Seek Joinder in an Arbitration     

Joinder is typically raised when several procedural or commercial concerns overlap:

Efficiency

If an additional party is central to the dispute, resolving the claims against all relevant parties in a single proceeding avoids duplication of effort, evidence, and cost.

Consistency

Separate proceedings against related parties risk inconsistent findings on the same facts. A tribunal hearing evidence in one arbitration may reach a different conclusion than a tribunal in another, even on identical issues

Finality

A single award binding all relevant parties provides finality. Without joinder, an award may leave unresolved questions about the liability of non-parties.

Avoiding Procedural Manoeuvring

Parties sometimes structure transactions to place assets or liabilities in entities that are not signatories to the arbitration agreement. Where the rules allow, a joinder can address this.

3. When Joinder Is Available Under the SIAC Rules

Rule 7 of the SIAC Rules 2025 (7th Edition) governs joinder. A party may be joined to an arbitration if:

1. The additional party has consented to joinder; or
2. The additional party is prima facie bound by the arbitration agreement.

“Prima facie bound” means that, on a preliminary assessment, there is a reasonable basis to conclude that the additional party is bound by the arbitration agreement, even if the additional party disputes this. The standard is not proof on the balance of probabilities at this stage, but is a threshold assessment.

Timing

The SIAC Rules distinguish between joinder before and after the tribunal is constituted:

• Before constitution: An application for joinder is decided by the Court of Arbitration (SIAC’s administrative body).
• After constitution: An application for joinder is decided by the tribunal, after consulting with all parties (including the proposed additional party).

The timing affects procedure but not the substantive requirements. In either case, the additional party must have consented or be prima facie bound.

Timing	Who Decides	Relevant Rule
Before tribunal constitution	Court of Arbitration	Rule 7.1
After tribunal constitution	Tribunal (after consulting all parties)	Rule 7.8

4. If You Want to Join an Additional Party

Step 1: Assess whether Joinder is available

Before applying, consider:

• Is the additional party bound by the arbitration agreement? This may be because the party signed the contract, is a successor or assignee, or is bound by principles such as alter ego, agency, or group of companies doctrine.
• Has the additional party consented? Consent may be express (in writing) or implied from conduct. If the additional party has participated in related proceedings or correspondence without objecting, this may support an inference of consent, though express consent is preferable.
• Is joinder tactically appropriate? Joining a party adds complexity. Consider whether the additional party’s participation is genuinely necessary or whether the dispute can be resolved without them.

Step 2: Prepare the Request for Joinder

A Request for Joinder under the SIAC Rules must include:

• The name, address, and contact details of the additional party
• A copy of the arbitration agreement under which the additional party is alleged to be bound
• A description of the basis on which the additional party is alleged to be bound (e.g., signatory, alter ego, assignment)
• A statement of the claims against the additional party, including the nature of the dispute and the relief sought
• The registration fee prescribed by SIAC

Step 3: Submit the Request for Joinder

If the tribunal has not yet been constituted, submit the Request for Joinder to SIAC. SIAC will notify the additional party and invite a response.

If the tribunal has been constituted, submit the application to the tribunal (with a copy to SIAC and all parties). The tribunal will determine the procedure for the application, which typically includes an opportunity for the additional party to respond.

Step 4: The Decision if the SIAC Court or Tribunal

The Court of Arbitration (before constitution) or the tribunal (after constitution) will determine whether joinder is granted. If granted, the additional party becomes a full party to the arbitration with all attendant rights and obligations.

5. If You Have Been Joined to an Arbitration

If you have received notice that a party is seeking to join you to an ongoing SIAC arbitration, you have several options.

Understand the Basis for joinder

Review the Request for Joinder carefully. The applicant must establish that you are prima facie bound by the arbitration agreement or that you have consented. Consider:

• Did you sign the contract containing the arbitration agreement?
• Are you a successor, assignee, or affiliate of a signatory?
• Is the applicant relying on alter ego, agency, or group of companies doctrine?
• Have you taken any steps that could be construed as consent?

Decide whether to Contest the Joinder

• You are not bound by the arbitration agreement (and have not consented)
• The prima facie standard is not met
• Joinder is procedurally improper (e.g., the application does not comply with the rules)

You may contest joinder on the grounds that:

Contesting joinder does not preclude you from also contesting jurisdiction on the merits if joinder is granted. A party joined over its objection may reserve its right to challenge the tribunal’s jurisdiction in the award or in subsequent proceedings.

Participate in the Joinder Application

Whether you contest or accept joinder, you should participate in the process. Failing to respond may result in joinder being granted by default. Even if you intend to challenge jurisdiction later, engaging with the joinder application allows you to put your position on record.

If you are…	Consider…
A signatory to the arbitration agreement	Joinder is likely to be granted; focus on the substantive defence
A non-signatory but affiliated with a signatory	Assess the strength of the alter ego / group of companies argument; contest if the connection is weak
Wholly unconnected to the arbitration agreement	Contest joinder vigorously; the prima facie standard should not be met

6. How the Tribunal and Court of Arbitration Decide Joinder Applications

The decision-maker applies a prima facie standard. This means the question is not whether the additional party is definitively bound by the arbitration agreement, but whether there is a sufficient basis to proceed on that assumption.

Factors typically considered include:

• The wording of the arbitration agreement and whether it extends to affiliates, successors, or assigns;
• The corporate relationship between the additional party and the existing parties;
• Whether the additional party participated in the negotiation, performance, or termination of the contract;
• Whether the additional party has conducted itself in a manner consistent with being bound; and
• The procedural stage of the arbitration and whether joinder would cause prejudice.

If joinder is granted, the additional party becomes a full party to the arbitration. It may file submissions, present evidence, examine witnesses, and is bound by the award.

If joinder is denied, the arbitration proceeds without the additional party. The applicant may need to commence separate proceedings if it wishes to pursue claims against that party.

7. Joinder vs Consolidation vs Multiple Contracts

These three mechanisms address related but distinct situations:

Mechanism	What It Does	When to Use
Joinder (Rule 7)	Adds a party to an existing arbitration	When a non-party is bound by the arbitration agreement and should be included
Consolidation (Rule 8)	Combines two or more separate arbitrations into one	When separate arbitrations involve common issues and should be heard together
Multiple Contracts (Rule 6)	Allows claims under multiple contracts to be brought in a single arbitration from the outset	When disputes arise under related contracts with compatible arbitration agreements

In short, joinder concerns parties, consolidation concerns proceedings, and multiple contracts concerns claims.

In practice, these mechanisms may interact. For example, a party may commence an arbitration under multiple contracts (Rule 6), then seek to join an additional party (Rule 7), and separately apply to consolidate with another pending arbitration (Rule 8).

8. Drafting Considerations

For parties negotiating arbitration clauses, the scope of joinder depends heavily on the wording of the clause and the relationships between the parties.

Facilitating Joinder of Parties in your Contracts

If the transaction involves multiple parties or related entities, consider:

• Including all relevant parties as signatories to the arbitration agreement
• Expressly providing that affiliates, successors, and assigns are bound by the arbitration agreement
• Using identical arbitration clauses across related contracts
• Including a provision expressly permitting joinder of non-signatories in defined circumstances

Restricting Joinder of Parties in your Contracts

If a party wishes to limit the risk of being joined to arbitrations involving affiliates:

• Ensure the arbitration agreement is limited to the named signatories
• Avoid language extending the clause to “affiliates,” “related parties,” or “successors”
• Maintain clear corporate separation between related entities

Conclusion

Joinder under the SIAC Rules allows parties to bring additional parties into an arbitration where those parties are bound by the arbitration agreement or have consented. The mechanism promotes efficiency and consistency, but requires careful assessment of whether the prima facie standard is met.

For parties seeking joinder, the key is demonstrating a sufficient basis for concluding that the additional party is bound. For parties resisting joinder, the focus is on showing that no such basis exists. In either case, early engagement with the process is essential.