Quick search by citation:

18 U.S. Code § 3597 - Use of State facilities

(a) In General.—
A United States marshal charged with supervising the implementation of a sentence of death may use appropriate State or local facilities for the purpose, may use the services of an appropriate State or local official or of a person such an official employs for the purpose, and shall pay the costs thereof in an amount approved by the Attorney General.
(b) Excuse of an Employee on Moral or Religious Grounds.—
No employee of any State department of corrections, the United States Department of Justice, the Federal Bureau of Prisons, or the United States Marshals Service, and no employee providing services to that department, bureau, or service under contract shall be required, as a condition of that employment or contractual obligation, to be in attendance at or to participate in any prosecution or execution under this section if such participation is contrary to the moral or religious convictions of the employee. In this subsection, “participation in executions” includes personal preparation of the condemned individual and the apparatus used for execution and supervision of the activities of other personnel in carrying out such activities.