Pre-employment screening including perusing social media of applicants, if available, is a common practice. However, once employees are hired, if said employees are effective at doing their jobs, I don't see how it could be viewed as discriminatory for an employer to look at employees' social media they participate in in their non-work hours and fire them for comments, beliefs, statements, etc (that's aren't illegal) because they don't align with corporate beliefs. I know it happens, but it's a shameful affront to a person's autonomy and individuality.