What is a field of membership? A field of membership must meet certain requirements and be approved by the NCUA. It is comprised of a group of members that share a specific bond, perhaps the same church, community or labor union. These groups will deposit money into share accounts, helping support one another through bond interaction. Contact Us For more information regarding field of membership or would like to join a federal credit union, contact Brownsville credit union branch of Valley Federal Credit Union at (956) 546-3108 or the Harlingen branch at (956) 425-5668.