The word club is a singular entity. Therefor "is" is correct.
The social club is holding a bake sale...
We are holding a bake sale for the social club...
In the US, "is". In the UK, I often hear "are" used since the social club is a reference to more than one person and is not thought of as an entity unto itself. So I think either is correct, depending on the locale.
Is, because a social club is one thing. If you said the members of the club were doing it, it would be are.
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It is "IS".
Our social club IS/ARE starting up a bake sale.
