ordination certificates 

Official government documents issued in China and Japan from time to time certifying a person's eligibility to enter the monastic Order (Saṃgha). At times, the purpose was to limit entrance into the order to prevent those who simply wished to evade taxes and corvée labour obligations from using ordination to obtain these ends. At other times, such as periods of national emergency, the government sold great quantities of ordination certificates as a quick means of raising revenues. Such was the case in China when the An Lu-shan Rebellion broke out in 755.

A Dictionary of Buddhism, Oxford University Press, 2003, 2004 (which is available in electronic version from answer.com)