H1B RFE i129 form

今天收到律师的通知，说他们收到了H1B rfe的通知，说他们正在review。我上uscis的网站查了一下，信息如下：“[align="center"]On August 28, 2017, we mailed a request for additional evidence for your Form I-129, Petition for a Nonimmigrant Worker, Receipt Number XXXXXXXXX[/align]” 请问各位这具体是一个什么事情呢？求有经验的同学解答，跪谢！