The purpose behind the rule is to ensure that the staffing agencies are keeping you compliant. As your sub-contractor, they need to be conducting outreach according to the federal contractor regulations. The notice itself is not the most critical issue. As a federal contractor, it is your obligation to ensure that the staffing agency is following the regulations, as though you were conducting the outreach for yourself.
You can use this OFCCP audit checklist to ensure you're doing what is required to maintain OFCCP's regulations including VEVRAA, Section 503, and EO 11246. Or request a demo to streamline your compliance and recruiting efforts.