One needs to also need to check underlying contracts, documentation etc. But, following pointers may be looked into while looking for potential defenses:
A. Generally speaking, it is likely that said association had provided by way of sponsorship to corporate / company in given scenario. And if yes, 100% of service tax was payable under RCM by the corporate / company and not by such association.
B. Service tax was applicable only if some services were provided for a consideration & not otherwise. For understand this better, attention is invited to Circular No. 127/9/2010-ST (bearing F. No. F. No. 354/314/2017-TRU) dated Dated 16-8-2010.
These are ex facie views of mine and the same should not be construed as professional advice / suggestion.