The "Main Street Depositor Protection Act" proposes to significantly expand deposit insurance coverage for noninterest-bearing transaction accounts at both insured depository institutions and credit unions. This legislation aims to enhance financial stability and promote economic growth by providing an additional layer of protection beyond the existing standard maximum deposit insurance amount (SMDIA). Under the bill, the Federal Deposit Insurance Corporation (FDIC) is mandated to establish a new maximum insured amount for these specific accounts. This amount must be not less than the SMDIA and not more than $5,000,000 , determined based on factors like financial stability and the safety of the Deposit Insurance Fund. Once set by rule, this insurance amount cannot be changed without an Act of Congress. Crucially, this expanded coverage specifically excludes accounts held at global systemically important bank holding companies and insured branches of foreign banks, though these institutions would still be covered by the standard insurance limits. For credit unions, the National Credit Union Administration Board (NCUAB) would extend similar insurance for noninterest-bearing transaction accounts, aligning the maximum insured amount with the FDIC's determination. The bill defines a noninterest-bearing transaction account as one that accrues no interest, allows easy withdrawals, and does not require advance notice for withdrawals. The legislation also includes a 10-year transition period during which the FDIC and NCUAB must gradually incorporate these newly insured amounts into their respective deposit insurance fund calculations. Additionally, insured depository institutions with total assets of $10 billion or less are exempt from certain special assessments or assessment increases related to this expanded coverage during the transition.