Many different actions and behaviors can be considered discriminatory. This is a legal term which refers to injustices far beyond simple teasing and genuine misunderstandings.
Below are several possible examples of gender identity discrimination:
An employee is fired shortly after announcing their plans to transition.
Management will not allow an employee to use the restroom which conforms to their gender identity.
Coworkers will only refer to a trans employee by their deadname.
A trans employee is being threatened or intimidated by their supervisor.
Insensitive jokes, slurs and sexual remarks are considered the norm in a workplace culture.