Section 19(5) in Bengal Trade Union Regulations, 1927
(5)Where the trade union is a federation of unions, and the member of unions affiliated it at any time during the financial year did not exceed 50, 15 or 5, respectively, the audit the accounts of the federation may be conducted as if it had not at any time during the year had a membership of more than 2,500, 750 or 250, respectively.
