Here's why:
* "Your" is a possessive pronoun: It indicates ownership, belonging to the person being addressed.
* "Employees" is the subject of the sentence: It refers to a group of people.
The sentence should be:
* "Employees must wash their hands." This uses the correct pronoun "their" to refer to the employees.
The sentence is now grammatically correct and clearly states that all employees are required to wash their hands.