Pandemic Anti-Monopoly Act of 2020 This bill places a moratorium on certain mergers and acquisitions during the COVID-19 (i.e., coronavirus disease 2019) pandemic. Specifically, the bill prohibits certain transactions such as acquisitions (1) by firms with over $100 million in revenue; (2) by financial institutions or equity funds with over $100 million in capitalization; and (3) involving firms with exclusive patents pertaining to COVID-19 pandemic-related production, manufacturing, distribution, or infrastructure. However, a waiver may be granted if the participating firms demonstrate that the transaction will advance critical national security, economic, or public health interests during the emergency. Further, the bill establishes a legal presumption against a transaction that may pose a risk to the government's ability to respond to the national emergency declared due to COVID-19.