Without a little more detail about what affidavit is being required from whom, and without knowing the requested contents of that affidavit, it’s hard to provide much detail here. But, looking at the California Civil Code sections regarding construction payments, mechanics lien claims, and stop notices – there is not statutorily required affidavit for subs or suppliers to list out their own subcontractors or vendors.
However, note that if it’s required under the contract – that means it’s a requirement. Even when there may be no statutory basis for the exchange of a document, if the parties have agreed to use it via contract, then that document will be required.
Also, note that since AB 1701 was passed (then codified as California Labor Code § 218.7), subs and suppliers must provide certain payroll information and sub/vendor information up the chain, if requested.