I agree with Erin that it sounds more like an overload payment than an augmentation, but to complicate things a bit further it might also be an increment. An increment is a component of pay, rather than an earnings type.
Human Resources should be consulted to determine whether it should be paid as an increment, augmentation or overload. It is ultimately their decision.
From an effort reporting perspective, the first two are considered part of Institutional Base Salary, are added to the individual's Notice of Appointment, and the earnings would be brought into ECRT. Overload earnings are not part of IBS. Overload pay is not brought into ECRT and, according to the Uniform Guidance, would require sponsor approval to be charged to a project.
~ David Hagen