Quick search by citation:

6 U.S. Code § 392 - Personal services

The Secretary
(1)
may procure the temporary or intermittent services of experts or consultants (or organizations thereof) in accordance with section 3109 of title 5; and
(2)
may, whenever necessary due to an urgent homeland security need, procure temporary (not to exceed 1 year) or intermittent personal services, including the services of experts or consultants (or organizations thereof), without regard to the pay limitations of such section 3109.