The U.S. Senate and House of Representatives, 38th Congress, 2nd Session wrote and submitted into record it's advice "it has become justifiable and necessary that the President should...resort at once to measures of retaliation...and that the executive and military authorities of the Unites States are hereby directed to retaliate upon the prisoners of the enemy..."
I don't know to what extent this went into laws or policies. The Union prisoner of war camps surely had the means to feed and take care of Confederate prisoners, the facts show in large numbers they did not, to their fullist abilities, do so. I can guess they purposely kept many Confederates in a state of poor health in case they were exchanged, to keep them from being able to immediately rejoin the Confederate ranks, but that is a guess. Likewise could be said of Confederate authorities; but does there exist a document, such as Bill S.R. 97, in the Confederate records?