The first three months of a new hire's in a workplace are often referred to as the employee's "probation period", and it is exactly what it sounds like. These three probationary months are there for the employee to prove that they were the right hire for the job. During these 90 days, new hires are expected to bring in their A-game, work as hard as they can to show their worth, and prove to management that they are worth keeping, without a single doubt.
An employee who fails to do so by the time the probation period ends will most likely be let go, without the company having to provide a severance package, a notice period, or anything else a long-term employee is eligible for.
However, most employers forget that this probation period is also there for the workplace to prove it's worth it to the new hire. The new employee also gets these three months to test and judge the workplace to see if it fits their expectations. Everything that applies to the employee also applies to the employer, including the end result: if the employee isn't satisfied with the workplace, they can leave immediately, no questions asked.
So, when the boss featured in this post on Reddit's r/antiwork decided to extend a new employee's probation period by another 90 days, he was doing so on both ends. If the workplace isn't yet sure about the new hire's value to the company, extending the probation period means that both parties can still cut ties at any point.
That is exactly what the employee did. Being told that she still didn't prove her worth in the company was a key sign for her that this was not a job she should keep, and luckily, she already had another offer at hand. When she sent her boss a resignation letter without any notice, he threatened to report her for breaking their contract. A contract that doesn't apply since he decided to extend the probation period…
Basically, he has no leg to stand on.