Enforced by multiple agencies, especially US Department of Justice and the Department of the Treasury (Internal Revenue Service, and Financial Crimes Enforcement Network - FinCEN).

http://www.fincen.gov/statutes_regs/patriot/index.html

In relation to financial institutions, the Patriot Act dramatically reduces restrictions on law enforcement agencies' ability to search telephone, e-mail communications, financial, and other records, as well as expanding the Secretary of the Treasury's authority to regulate financial transactions, particularly those involving foreign individuals and entities.

Key provisions affecting financial institutions: Title III of the Act, International Money Laundering Abatement and Financial Anti-Terrorism Act of 2001, facilitates the prevention, detection and prosecution of international money laundering and the financing of terrorism. It primarily amends portions of the Money Laundering Control Act of 1986 (MLCA) and the Bank Secrecy Act of 1970 (BSA) by 1) strengthening banking rules against money laundering 2) expanding record keeping and reporting requirements 3) increasing penalties for currency smuggling and counterfeiting. See BSA/AML entry for details.

USA PATRIOT ACT full text

All US residents and businesses operating in the United States.

http://en.wikipedia.org/wiki/Patriot_Act