Can you fire an employee for a post on social media that disparages your business? It depends. Before you pick up that pink slip, make sure that you understand the limits of what is supported by the National Labor Relations Bureau (NLRB).
Protected Concerted Activity
Whether what is being said is fair or not, if employees are griping about the workplace together on somebody's social media page, that probably counts as protected concerted activity -- which is the basis of unionization. It doesn't matter if they are in a union or not. Employees are free to discuss almost anything together:
their working conditions
their wages or raises
their uniforms or dress code
their employer's rules of conduct
the hours or shifts they have to work
management's conduct at work
The important things to examine is whether or not there is a discussion being held -- or an attempt at one, at the very least. If there is, it's illegal for you to retaliate by firing anybody involved.
General Venting And Grousing
If an employee takes to social media just to rant and grouse about conditions on his or her own personal page, without trying to engage other employees in a discussion, that's not a protected activity and you can fire him or her for the action.
For example, the NLRB upheld the suspension of a department store's employee after he made some comments about the assistant manager's "tyranny." The NLRB judged that the employee's comments were about a personal gripe and not designed to foster a group action with his co-workers.
Customer And Company Mocking
You also have the right to take action if the employee is just generally mocking your company or the customers. While the employee has a right to his or her individual opinions, the right to express those opinions stops if it runs counter to your company's interests and could either damage your customer base or make your employee ineffective.
For example, a caseworker for a child-protective services agency put some half-serious, half-mocking posts online about what she believed should be some mandated rules. Her rancor and statements effectively ruined her credibility as a neutral party in cases of abuse, making her useless as a witness for the agency. The NLRB upheld her firing.
In another case, a salesman at a high-end car dealership posted a video of an accident that occurred during a test drive to mock his employer. Even though the judge found the dealership's social media policy too broad because it mandated that employees not speak ill of the company, the firing over the video -- which was done purely for amusement and not to further discussion among employees -- was upheld.
This is a fast-moving area of the law and constantly evolving, so it pays to be cautious before you take action. If you have any questions about your right to terminate someone's employment over an online post, talk to legal services first.