Can Companies Control What You Say After You Leave?

anonymousByGoodReason asks: "I worked for a company doing IS support for about 6 years. It's been over a year since I've left them, and because I still have friends there, I keep an eye on the stock price and message boards, etc. on Yahoo! As it turns out, several ex-employees are up there, some with fair opinions of the company, some with not so fair. Conversation on the board turned to the ex-employees, and I posted my opinion, and why I left. The reason was less than glowing, but I really didn't go into too much depth - basically I gave the general overview. What I've found out now, is that the auditing department of that company has since been keeping track of those message boards, and has identified me. I've been told that they may speak to me, and may also talk to the company I currently work for." Umm...Yahoo!'s message boards are public, and the guy no longer works for them (and had no contractual obligations to stay silent when he left), so what precedent gives his ex-company the right to audit his opinions?

"My question is this - because I left the company of my own free will, and had never signed an agreement that said 'I will only say nice happy things about this company after I leave'... what recourse, if any, do they have to my statements? Their stock price has been rock-bottom before I posted, and actually was gaining, albeit slowly, as the postings went forward, so they didn't lose any money because of statements that I made. Should I be concerned? Am I no longer entitled to have an opinion about a place where I used to work?"