Examine O.XII of CPC and you'll find your answer. Your post is vague as to how exactly the Claimant has 'relied' upon the document. The exact mode of reliance is the heart of the matter.

Examine applicability of CPC to arbitration proceedings and pull out judgments on this point. Pull out judgments on the point of procedure is handmaid of justice and not its mistress.

As a last resort if nothing works you can file a notice to admit documents and in case the tribunal is inclined to reject it (which it appears likely in your facts and circumstances), you can request the tribunal to rule on this application as part of the final award. Since only your final award is appealable under the Act and not these interlocutory orders and directions.

In an arbitration, Respondents filed the documents as additional documents. However, the tribunal rejected the documents because they had to be filed along with written statement or counter claim as laid down under Order 8 CPC and Order 11 Commercial Courts Act. Further, no reasonable cause was given for the delay. Later, they also tried to bring the documents again through cross examination during which new documents can be produced. However, the said move was rejected. Till this time, the claimants always objected to the Respondent's move to produce additional documents because of unreasonable delay.

However, later the claimants themselves relied upon the said documents of the Respondent during a cross examination. Can it be said that now those documents have been admitted by the claimants against themselves.

Kindly let me know if there is any authority on this.

Thanks