The United Prisoners Union (UPU), formerly known as the California Prisoners Union (CPU, Dec 1970-Oct 1971), grew out of a movement in the early 1970's which recognized that real changes had to be made within the inhumane prison system. The original work UPU undertook was to organize prisoners and ex-prisoners into labor unions that could make demands such as a minimum wage scale, workmen's compensation, safer working conditions, better medical care, etc. Initially, UPU's focus was in securing reforms as a means of bringing about change inside the prison system. Later, UPU realized that reforms in themselves are neither a goal nor a solution but rather a tool to use in bringing about the change necessary to end the cause for prison itself. For more information, see UPU's newspaper, The Anvil. 

In October, 1971, several UPU members broke from San Francisco Local #9 and formed a separate entity, the Prisoners Union. For more information, see the Prisoners Union Collection.