Section 9. If the bureau determines that a taking agency or relocation agency is proceeding with a project in disregard of a relocation plan approved under section five, and that relocation assistance being given is inadequate, the bureau shall so notify the relocation agency and the taking agency in writing, and may suspend its approval of the plan. Upon receipt of written notice of such suspension, the taking agency shall not further displace occupants until the bureau notifies it in writing that such suspension is withdrawn. Written notice of suspension shall be sent by registered mail, and shall state the specific reasons for such suspension.