The Winnebago Tribe, Omaha Tribe and Santee Sioux Nation of Nebraska filed lawsuits Tuesday.
The Ponca Tribe of Nebraska and Knox County sued April 25.
"The four Nebraska Tribal Chairmen and their Councils collaborated to assure that their efforts together strengthen and emphasize the importance of relief for their tribal governments and to underscore the impact on their members," said their attorney, David Domina of Omaha.