Here you go, Captain Smugface (and everybody else who wants to know):

Section 25: Scheduling 25-16

3. Crew Move-Up
In the event of an uncovered flight segment, trip, or the absence of a
pilot, a trip may be reassigned to any Regular, Relief, or Reserve pilot
who is legal, qualified, and available to fly the uncovered flight segment
or trip. When assigning or rescheduling a pilot for a move-up it must be
made with the pilot’s consent, under the following guidelines:

a. Restore pilot to his original trip as soon as possible if economically
and logistically feasible.

b. Assign pilot to a trip or open flight segments, which will return the
pilot closest to the return date/time of their original trip.

c. If accepted the pilot receives one and one half (1.5) additional hours
of pay and credit above minimum guarantee per duty period of the
move-up trip pairing, in addition to pay protection for his original
trip pairing.

Example: A pilot is scheduled for a trip pairing with a pay credit
of 20 hours. He accepts a move-up trip pairing with a pay credit
of 15 hours that contains two duty periods. The pilot is paid above
monthly guarantee three (3) hours, and in addition, maintains the 20
hour pay credit protection associated with his original trip pairing.
The move-up pairing over-blocks to 15:30. The pilot is paid 20 hours
plus the three (3) hours above his monthly guarantee.