That varies wildly by jurisdiction. The article describes the various prerequisites in a couple of Australian states/territories (most of whom include advanced notice), and in the EU it goes even further than that, requiring advanced notice and having severe limitations in what your employer can actually monitor. An example court case:
> On September 5, 2017, the Grand Chamber of the European Court of Human Rights (ECtHR) ruled that a private company's decision to dismiss an employee, after monitoring and accessing his instant messages sent from the workplace, violated the employee's right to respect for private and family life
To elobarate on that, the hurdles for monitoring employees are really high. It is always illegal to do it secretly and conversations etc are considered private even if you're in the office and talk with collegues. Also worker's councils hate that stuff and a company would have a really bad time with theirs.
> On September 5, 2017, the Grand Chamber of the European Court of Human Rights (ECtHR) ruled that a private company's decision to dismiss an employee, after monitoring and accessing his instant messages sent from the workplace, violated the employee's right to respect for private and family life
https://www.theguardian.com/law/2017/sep/05/romanian-chat-me...