The $20 billion PenFed is re-joining CUNA after a 12-year hiatus.
The trade association is the fourth to publicly reject CUNA's dual membership requirement.
Credit unions in the Carolinas, California and Nevada gear up for membership cost hikes.
CUNA and Carolinas League out $340,000 in membership dues with loss of nation's second largest credit union.
CUNA's largest affiliated credit union, the $27 billion State Employees' Credit Union of North Carolina, will not renew its membership in 2014.
Site will allow employees at member credit unions to collaborate, and will include streamlined event registration with multiple payment options.