Citigroup's Ex-Exec May Face SEC Action  NEW YORK (Reuters) - Citigroup Inc. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=C.N target=/stocks/quickinfo/fullquote"&gt;C.N&lt;/A&gt; on Friday said  U.S. securities regulators may recommend enforcement  proceedings against the former head of Citigroup Global  Investment Management.