IEX is planning on listing companies so they were sued by NASDAQ exchange. The part I do not understand is that the legal action is for patent infringement. Isn't exchange behavior (algorithms?) regulated by the SEC? Here is a URL to one story: https://www.marketwatch.com/story/flash-boys-exchange-iex-hits-back-at-nasdaq-lawsuit-2018-05-30
Nasdaq cannot legally stop IEX from listing companies, so they are applying pressure by suing for patent violations. My guess is Nasdaq hopes IEX will settle the patent suit by agreeing not to list companies. According to the article: Nasdaq claims that IEX is infringing on seven patents that relate to “..., multi-parallel order processing, matching engine performance, and data feed optimizations,” according to Nasdaq’s announcement of the suit in March." There is no way Nasdaq can know that IEX is violating these patents without having seen the IEX source code.