Department of Homeland Security 'United States Citizenship and Immigration Services' Budget Overview (Fiscal Year 2018 Congressional Justification) [open pdf - 2MB]
From the Component Overview: "The U.S. Citizenship and Immigration Services (USCIS) is comprised of the following mission-oriented programs that support achievement of the DHS strategic missions, goals, and objectives.  'Employment Status Verification': The Employment Status Verification (E-verify) program enables authorized employers to quickly and easily verify the work authorization of their newly hired employees. [...]  'Immigration Examinations Fee Account': The Immigration Examinations Fee Account (IEFA) is the primary funding source for USCIS. Fees collected from immigration benefit applications and petitions are deposited into IEFA and are used to fund the cost of processing immigration benefit applications and associated support benefits, as well as to cover the cost of processing similar benefit requests for applicants without charge, such as refugee and asylum applicants.  'H-1B Nonimmigrant Petitioner Account': The H-1B Nonimmigrant Petitioner Account supports activities related to the adjudication of employment-based petitions for nonimmigrant workers seeking an H-1B visa. This program allows U.S. employers to temporarily employ foreign workers in specialty occupations.  'Fraud Prevention and Detection Account': The Fraud Prevention and Detection Account supports activities related to preventing and detecting fraud in the delivery of all immigration benefit types. The program leads efforts to identify threats to national security and public safety, detect and combat immigration benefit fraud, and remove systematic and other vulnerabilities."
U.S. Department of Homeland Security: https://www.dhs.gov/