A method, a system, and a non-transitory storage medium are described in which an access and mobility management function (AMF) assignment service is provided. A network device receives an assignment policy for selecting an AMF from a group of available AMFs, wherein the assignment policy includes network slice priorities for available network slices in the RAN; stores the assignment policy; receives, during a registration procedure initiated by an end device, Network Slice Selection Assistance Information (NSSAI); identifies, from the NSSAI, multiple single-NSSAIs (S-NSSAIs); and selects, based on the assignment policy, an AMF for a highest priority S-NSSAI, of the multiple S-NSSAIs.