Zheng-de: Year 16, Month 5, Day 9
13 Jun 1521
Under the old system, when the yi from the various islands in the ocean came to offer tribute through Guang-dong, their credentials were verified and advice was memorialized. Their cargo was then taxed (榷), and the proceeds were used by the state. However, for a long period, seekers of ill-gotten gain, under the pretence of coming to offer tribute, came and went at irregular intervals. Also, some offices profited from the taxes and did not enforce the prohibitions. This gave rise to internal squabbling and the people suffered much thereby. At this time, the defence officials memorialized. It was Imperially commanded that in future when foreign yi came to offer tribute, their credentials were to be examined and only if it was ascertained that they were coming at the specified tribute frequency were they [to be received] and taxed in accordance with the regulations. Those private ships of evil persons which were not coming to offer tribute, those which came at other than the specified tribute frequency and traders who stated that they had been sent by various yi rulers were all to be refused and sent back.
Zhong-yang Yan-jiu yuan Ming Shi-lu, volume 70, page 86