61.113 - Private pilot privileges and limitations: Pilot in command.
(a) Except as provided in paragraphs (b) through (g) of this section, no person who holds a private pilot certificate may act as pilot in command of an aircraft that is carrying passengers or property for compensation or hire; nor may that person, for compensation or hire, act as pilot in command of an aircraft.
(b) A private pilot may, for compensation or hire, act as pilot in command of an aircraft in connection with any business or employment if:
(1) The flight is only incidental to that business or employment; and
(2) The aircraft does not carry passengers or property for compensation or hire.
Question now is:
Is your paycheck tied to your flightduty?
Yes --> Need CPL
No --> Need PPL
Safety, recurrent training, sound operational procedures, CRM... Thats a whole 'nother matter