Cal. Gov. Code § 84220

If a slate mailer organization receives a payment of two thousand five hundred dollars ($2,500) or more for purposes of supporting or opposing any candidate or ballot measure in a slate mailer, and the payment is received at a time when, if the payment were a contribution it would be considered a late contribution, then the slate mailer organization shall report the payment in the manner set forth in Section 84203 for candidates and committees when reporting late contributions received. The slate mailer organization shall, in addition to reporting the information required by Section 84203, identify the candidates or measures whose support or opposition is being paid for, in whole or in part, by each late payment.