When an employee bad-mouths the employer on social media

What can an employer do when an employee bad-mouths it on Facebook, Twitter, WhatsApp, YouTube or any other forms of social media?
We live in a day and age where social media has a huge influence on business. So much so that any negative comments may cause some major damage to the employer’s image and reputation.
So what can be done if an employee rips an employer apart on social media? The answer is simple: The employer can take action! 
An employee who bad-mouths an employer, including a manager or fellow-employees, can under South African law, be liable for damage claims and even dismissal.
The legal relationship between the employer and employee is one of good faith. There is therefore no reason for the employer to keep an employee who causes harm to the employer’s image. Instead, the employer may dismiss the employee for any bad comments on social media.
However, the employer must be warned that this does not apply if an employee is speaking the truth, regardless of how negatively the comments affect the company’s image. If an employee is dismissed for exposing the truth about the employer, then the employee will able to turn the tables and claim damages from the employer.
Therefore, before dismissing an employee, the employer must make sure that it is in the right and that it is not trying to cover an inconvenient truth. If the employer does, it will end up paying for it.