The Law of Riona Prime is a Kryptonian policy of non-interference that forbids any Kryptonian to directly interfere in the natural development of another race, for any reason.
Many millennia ago, the planet Riona Prime, the sole inhabited planet in the Riona System, was struck by a meteor and suffered global catastrophe as resources and infrastructure were utterly decimated. Millions had died, and millions more would likely perish during the rebuilding - in fact, it was doubtful that they even could rebuild. A Kryptonian task-force was in the system during the impact, and reported back to the Council of Twelve in which Krypton's experts predicted inevitable extinction for the Rionians. The Council made their decision to render aid to the Rionians in the form of a modified Entropic Power Module with minimal maintenance that would provided more than enough energy to rebuild, and to keep their support systems running long enough for that to happen.
A week later, the same Kryptonian task-force returned to Riona Prime and was shocked to discovered it had been further utterly devastated and without any survivors. It was revealed from the data recorded from the planet that Riona's different factions fought over the Module until they simply destroyed themselves. The lessons of Riona Prime led to the Kryptonians into believing that their interference with other races would have the same disastrous results, thus creating the need for a stringent non-interface clause. Which henceforth the Law of Riona Prime came to be.
Although Krypton upheld the Law of Riona Prime, the law was defied in life threatening cases. During the war against the Gibborim, Krypton temporarily uplifted the law.
Even after Krypton was destroyed, Kryptonian survivors such as Superman and Supergirl continued to uphold the Law of Riona Prime and forbid any surviving Kryptonian technology from falling into the wrong hands. The Law also caused some strain between Earth's nations over sharing Kryptonian technology. This became more problematic in concerning the Fortress of Solitude, which had been assaulted several times by forces in gaining access to its storehouse of Krypton's knowledge.
The Law of Riona Prime bears some similarities to the Prime Directive in the Star Trek franchise.