Nasdaq OMX is sending a message to firms weighing lawsuits related to trading losses in Facebook's initial public offering: winning won't be easy.

The exchange operator believes it is protected by its contracts with members and by its unusual legal status, which is rooted in its dual role as a regulatory body as well as a business that makes money running markets. Exchange officials in recent weeks have pointed out to analysts that Nasdaq has never been successfully sued over a trading error.