'Petition against the Expulsion of Guests') was a petition to Ying Zheng, King of Qin, written by Li Si in 243 BC.
During the Warring States period, it was common practice for learned men whose careers might have been frustrated in their homelands to travel to other countries in search of service and patronage.
Li Si himself was such an individual, having been born in the State of Chu but unable to progress in an official career there.
The initial policy of openness to outsiders changed in 244 BC, due to the controversy surrounding the Zhengguo Canal; the State of Han had dispatched Zheng Guo, a skilled engineer, to Qin on the pretext of helping them build an irrigation canal.
Subsequently, however, it was discovered that this was really a scheme by Han to weaken Qin by diverting its resources towards canal construction.