40 CFR § 1506.1 - Limitations on actions during NEPA process.
(a) Except as provided in paragraphs (b) and (c) of this section, until an agency issues a finding of no significant impact, as provided in § 1501.6 of this chapter, or record of decision, as provided in § 1505.2 of this chapter, no action concerning the proposal may be taken that would:
(1) Have an adverse environmental impact; or
(2) Limit the choice of reasonable alternatives.
(b) If any agency is considering an application from a non-Federal entity and is aware that the applicant is about to take an action within the agency's jurisdiction that would meet either of the criteria in paragraph (a) of this section, then the agency shall promptly notify the applicant that the agency will take appropriate action to ensure that the objectives and procedures of NEPA are achieved. This section does not preclude development by applicants of plans or designs or performance of other activities necessary to support an application for Federal, State, Tribal, or local permits or assistance. An agency considering a proposed action for Federal funding may authorize such activities, including, but not limited to, acquisition of interests in land (e.g., fee simple, rights-of-way, and conservation easements), purchase of long lead-time equipment, and purchase options made by applicants.
(c) While work on a required programmatic environmental review is in progress and the action is not covered by an existing programmatic review, agencies shall not undertake in the interim any major Federal action covered by the program that may significantly affect the quality of the human environment unless such action:
(1) Is justified independently of the program;
(2) Is itself accompanied by an adequate environmental review; and
(3) Will not prejudice the ultimate decision on the program. Interim action prejudices the ultimate decision on the program when it tends to determine subsequent development or limit alternatives.