54 U.S.C. § 102101

1. (a)
   1. (1)No natural curiosity, wonder, or object of interest shall be leased or granted to anyone on such terms as to interfere with free access by the public to any System unit.
   2. (2)The Secretary, under such regulations and on such terms as the Secretary may prescribe, may grant the privilege to graze livestock within a System unit when, in the Secretary’s judgment, the use is not detrimental to the primary purpose for which the System unit was created. This paragraph does not apply to Yellowstone National Park.
2. (b)The Secretary may grant privileges and enter into leases described in subsection (a), and enter into related contracts with responsible persons, firms, or corporations, without advertising and without securing competitive bids.
3. (c)No contract, lease, or privilege described in subsection (a) or (b) that is entered into or granted shall be assigned or transferred by the grantee, lessee, or licensee without the prior written approval of the Secretary.