Many of the present-day Agencies that exist, existed in previous forms or versions in the past, sometimes with different names. This can make tracking the legislation that created the agency listed in your syllabus a bit tricky. The best place to find the history of Agencies, and possibly the legislation that created them, is to check out the United States Government Manual which should give a short history of the agency and its legislative/executive authority.
Other options for locating agency history and legislation that brought an agency into being can be found in the list of links below.
When you do find the legislation that created the Agency, you may have to repeat several steps to find the US Code Citation or Statutes at Large citation so you can use that to look up the authorities granted the Agency in the Code of Federal Regulations.
Be sure to cover the following...
1. Identify the Agency(s) involved in the Supreme Court case.
2. Discuss the legislation or order that created the Agency(s) and the range of powers and responsibilities it was given in the enabling act that created it.
3. What ruling or other action taken by the Agency(s) gave rise to the case brought before the Supreme Court.