The National Environmental Policy Act (NEPA) was enacted in 1970 and established a process for the review of the environmental impact of projects within the federal purview. It also established the Council on Environmental Quality (CEQ), an office of the executive branch tasked with overseeing NEPA implementation. The law requires that Federal agencies prepare environmental assessments (EA) and (if required) environmental impact statements (EIS) for projects to assess their environmental impact.

While the law emphasizes environmental protection, it has been criticized for slowing the transition to renewable energy by causing delays in projects related to clean energy technology. Section 4.3 of the National Association of Environmental Professionals 2021 Annual NEPA Report says the following about the length of time for EISs completed in 2021 (NOI refers to notice of intent to prepare an EIS and NOA refers to the notice of availability of the EIS):

. . . final EISs prepared by all agencies combined had an average preparation time (from the Federal Register NOI to the EPA NOA for the final EIS) of 1,678 ± 1,589 days (4.6 ± 4.4 years[)].

The length of EIS review may be a significant factor in future US mining capacity for critical minerals. According to a report published by SNL Metals & Mining

. . . it takes on average seven to 10 years to secure the permits needed to commence operations in the U.S. To put that into perspective, in Canada and Australia, countries with similarly stringent environmental regulations, the average permitting period is two years.

In September of 2020 the Trump administration's CEQ updated the regulations regarding NEPA implementation. This update included setting a one year time limit on EAs and a two year time limit on EISs, though these time limits could be extended by a written order from the lead agency performing the NEPA review (the relevant section of the 2020 final rule is § 1501.10). In 2021 the Biden administration extended the deadline for agencies to update their procedures in accordance with the 2020 rule until September 2023. In 2022 the CEQ also issued a final rule reversing some of the 2020 changes in what it referred to as "Phase 1" revisions to the 2020 rule, with a "Phase 2" to follow. The "Phase 1" revisions did not remove the timeline requirement imposed in the 2020 rule.

In 2022 several House Republicans introduced a bill that would impose timelines for NEPA review of 18 months for an EA and 24 months for an EIS, which could not be extended without agreement from the project applicant.