The New York Stock Exchange has lashed out against plans by IEX Group to launch a new exchange, claiming its proposed rules are opaque and unfair.

NYSE Group, a unit of the Intercontinental Exchange, said in a comment letter to the Securities and Exchange Commission on November 12 that the proposed rules of IEX Group failed to explain in detail how the exchange would operate. It also said the group's signature feature-a speed bump to slow down high-speed traders-might end up giving some traders an advantage over others.