Which agency is responsible for enforcing federal tax laws in the United States?

The agency responsible for enforcing federal tax laws in the United States is the Internal Revenue Service (IRS). This organization operates under the Department of the Treasury and is tasked with administering and enforcing the tax code. The IRS oversees the collection of federal income taxes and ensures compliance with tax laws through various means, including audits and enforcement actions against those who do not fulfill their tax obligations.

While the Department of the Treasury plays a vital role in the overall financial and economic policy of the U.S. government, including overseeing the IRS, it is the IRS that specifically handles the enforcement of tax laws. The Federal Trade Commission focuses on protecting consumers and maintaining competition, while the Social Security Administration manages social security programs, neither of which involves tax law enforcement. Thus, the correct answer reflects the specific role of the IRS in the context of federal tax law.