34 C.F.R. § 650.34

In order to continue to receive payments under a fellowship, a fellow shall—

(a) Maintain satisfactory progress in the program for which the fellowship was awarded as determined by the institution of higher education;

(b) Devote essentially full time to study or research in the field in which the fellowship was awarded, as determined by the institution of higher education;

(c) Not engage in gainful employment during the period of the fellowship except on a part-time basis, for the institution of higher education at which the fellowship was awarded, in teaching, research, or similar activities approved by the Secretary; and

(d) Begin study under the fellowship in the academic year specified in the fellowship award.