U.S. Customs and Border Protection (CBP) is amending its regulations to implement new subsection 13031(b)(9)(D) of the Consolidated Omnibus Budget Reconciliation Act (COBRA), as amended by section 8002 of the Synthetics Trafficking and Overdose Prevention Act of 2018 (STOP Act). Among other things, the new subsection establishes a new fee for processing Inbound Express Mail Service items (Inbound EMS items), requires the United States Postal Service to pay a percentage of this fee to CBP on a quarterly basis, provides that Inbound EMS items that are formally entered are also subject to a merchandise processing fee, if applicable, and requires the Secretary of the Treasury to issue regulations regarding USPS's quarterly remittances to CBP. This rule also makes conforming amendments to CBP regulations.