Can Merrill Lynch fire an employee for speaking to the media?

My friend was fired from Merrill Lynch in Jacksonville, FL as a Financial Advisor at the Financial Advisory center for speaking to the media. Merrill Lynch must approve all outside business ventures and this Advisor told Merrill Lynch what he did and the head compliance manager, Donna Fairclothe approved it as an acceptable business venture. A year goes by. A news article comes out bashing his business venture which Merrill Lynch knew about and approved as ok to do outside of work. Donna Fairclothe, head compliance manager and the Financial Advisory center, informed him to shut down his outside company or be fired. He refused and defended himself to the news reporter and then the news reporter retracted the first article and wrote good things about his business venture. Donna Fairclothe and Brenda Godfrey, head of the FAC by this time terminated my buddy saying he went against company policy about speaking to the media. (They did this before the 2nd news article came out praising my friends outside business venture.) HIs outside business venture had no connection with Merrill Lynch. Was it legal for the Merrill Lynch to fire this employee over this? Is there any legal recourse he can do or bring to sue Merrill Lynch or the head managers responsible for his termination?