The U.S. Government Accountability Office (GAO) is known as "the investigative arm of Congress" and "the congressional watchdog." GAO supports the Congress in meeting its constitutional responsibilities and helps improve the performance and accountability of the federal government for the benefit of the American people.
"The PCAOB is a nonprofit corporation established by Congress to oversee the audits of public companies in order to protect the interests of investors and further the public interest in the preparation of informative, accurate and independent audit reports. The PCAOB also oversees the audits of broker-dealers, including compliance reports filed pursuant to federal securities laws, to promote investor protection."
These online resources are helpful when seeking information about taxes.