Amazon was penalized for excessive employee monitoring, insufficient data minimization, and failing to meet transparency and security requirements. Much of the GDPR fine centers on the hand scanners that are issued to warehouse employees.
The UK ICO guidelines specify that workplace monitoring must be disclosed to employees (along with its 'clearly defined' purpose), and the 'least intrusive' method must be used to accomplish the stated purpose.
By implementing an employee monitoring strategy that is inherently GDPR-equivalent to privacy, your organization will be better prepared for future data privacy obligations.