This question has divided the office into two camps. Camp 1 believes the correct way to indicate the relationship in this sentence is to use the client's name as a possessive, as in "When UltraGalactic's employees call the Customer Service line..." Camp 2 believes the apostrophe can be dropped because "UltraGalactic" is modifying "employees," and therefore the possessive is assumed. Frankly, I don't understand the uproar over typing two additional characters, but I'd appreciate your feedback.
Both are grammatically correct.
Indicates that the employees belong to UltraGalactic.
Indicates that employees are employees at UltraGalactic.