According to the prompt below, is the principal of law that is being broken is trade libel under defamation because he post on Facebook a statement that can harm or damage the business? I need some help with this. Thank you.

Sammyis a truck driver for a well-known national trucking/hauling company. Once, while on a delivery trip across country, he encountered a closed road which caused long delays. Sammy tried many times (unsuccessfully) to reach his employer's on-call dispatcher, because he wanted the dispatcher to notify the customer of the delivery delay.Once Sammy returned from the delivery trip, he discovered that the company's dispatch unit had an incomplete phone set-up. Sammy posts a rant on his personal social mediapage, where he complained about the employer's inability to handle basic technology installations.

Should the employer take action against Sammy for his social media post? Would the employer have grounds to terminate Sammy? Would Sammy have an argument against any disciplinary action taken against him?