Undoing NEPA’s Substantial Harm by Advancing Concepts that Kickstart the Liberation of the Economy Act of 2020 or the UNSHACKLE Act of 2020 This bill revises the environmental review process required under the National Environmental Policy Act of 1969 (NEPA), including by establishing deadlines for federal agencies to complete reviews of the environmental effects of proposed major federal actions; establishing penalties for agencies that do not comply with these deadlines; limiting the number of assessment documents required for proposed major federal actions, requiring agencies to reuse certain research or documents, and allowing agencies to adopt environmental documents prepared by states or third parties; requiring agencies to only consider alternatives to proposed actions that are technically and economically feasible; prohibiting agencies from considering whether proposed actions or alternatives to those actions will have an effect on climate change; and establishing requirements concerning the judicial review of NEPA cases.