The passenger list is part of the load manifest required under federal regulations for operators of "domestic, flag and supplemental" aircraft. see 14 CFR 121.693(e), below:

14 CFR Sec. 121.693 Load manifest: All certificate holders.

The load manifest must contain the following information concerning the loading of the airplane at takeoff time:
(a) The weight of the aircraft, fuel and oil, cargo and baggage, passengers and crewmembers.
(b) The maximum allowable weight for that flight that must not exceed the least of the following weights:
(1) Maximum allowable takeoff weight for the runway intended to be used (including corrections for altitude and gradient, and wind and temperature conditions existing at the takeoff time).
(2) Maximum takeoff weight considering anticipated fuel and oil consumption that allows compliance with applicable en route performance limitations.
(3) Maximum takeoff weight considering anticipated fuel and oil consumption that allows compliance with the maximum authorized design landing weight limitations on arrival at the destination airport.
(4) Maximum takeoff weight considering anticipated fuel and oil consumption that allows compliance with landing distance limitations on arrival at the destination and alternate airports.
(c) The total weight computed under approved procedures.
(d) Evidence that the aircraft is loaded according to an approved schedule that insures that the center of gravity is within approved limits.
(e) Names of passengers, unless such information is maintained by other means by the certificate holder.