The "Know Your American Customer Act" mandates that insured depository institutions and insured credit unions verify the citizenship or legal status of individuals seeking to open or maintain accounts. This legislation defines "lawful presence" as being a U.S. citizen, national, or an alien with an unexpired period of authorized stay in the United States. The bill aims to prevent individuals who are not lawfully present from accessing financial services and applies to natural persons opening accounts or those exercising substantial control over legal entities opening accounts. For new accounts opened 90 days after enactment, individuals must present specific documents such as a U.S. passport, birth certificate, green card, or a foreign passport with a valid Arrival/Departure Record (Form I-94) to prove their lawful presence. If an individual's temporary authorized stay expires, the institution must first allow 30 days of full access, followed by a 60-day period where only incoming deposits are permitted, before ultimately closing the account if updated documentation is not provided. Covered institutions face civil penalties for non-compliance, though safe harbors exist for good-faith efforts to adhere to the law. The Secretary of the Treasury, through FinCEN, is tasked with enforcing these provisions and must issue interim guidance within 30 days and final regulations within 90 days of enactment. Importantly, the bill explicitly supersedes any conflicting state laws regarding lawful residency verification by financial institutions. Furthermore, the legislation introduces criminal penalties for individuals not lawfully present in the U.S. or under a removal order who open or maintain an active account, potentially facing fines up to $1,000,000, imprisonment for up to one year, or both, with exceptions for pending asylum applications or recently expired authorized stays.