It's probably not a good idea. The National Labor Relations Act (NLRA) prohibits employers from retaliating against employees for communicating with each other about the terms and conditions of their employment. And, this protection extends to communications online as well as those made in person or by other means. Recently, the National Labor Relations Board has filed complaints against two employers that disciplined employees for making critical comments about managers and the company on Facebook and Twitter. To learn more about what you can and can't do in response to employee's online posts, see Nolo's article Employee Posts on Facebook, MySpace, Twitter, and Blogs.