Landowners' Right to Due Process in Rehearings at FERC Act of 2021 This bill revises the rehearing process for petitioners aggrieved by an order issued by the Federal Energy Regulatory Commission (FERC) with respect to natural gas pipeline projects. Specifically, the bill sets forth a 60-day deadline for FERC to respond to a rehearing request from a petitioner. During this time, FERC is prohibited from authorizing construction-related activity that is related to the order, and the holder of a certificate of public convenience and necessity that is the subject of the order may not exercise the right of eminent domain to acquire land or other property to carry out the pipeline project.