The U.S. Federal Trade Commission is inviting public feedback on a request made by Scott Sheffield, the former CEO of Pioneer Natural Resources. Sheffield is seeking to challenge an FTC ruling related to Exxon Mobil Corp's acquisition of Pioneer. The ruling prohibits Exxon from involving Sheffield in the company's board of directors or in an advisory role, following the acquisition of Pioneer for $59.5 billion by the top U.S. oil company, Exxon.