If a lead agency finds that an EIS or finding of no significant impact for a project would not be prepared by the federal agency by the time when the lead agency will need to consider an EIR or negative declaration, the lead agency should try to prepare a combined EIR-EIS or negative declaration-finding of no significant impact. To avoid the need for the federal agency to prepare a separate document for the same project, the lead agency must involve the federal agency in the preparation of the joint document. The lead agency may also enter into a Memorandum of Understanding with the federal agency to ensure that both federal and state requirements are met. This involvement is necessary because federal law generally prohibits a federal agency from using an EIR prepared by a state agency unless the federal agency was involved in the preparation of the document.