The Health Care Reform law (The Patient Protection and Affordable Care Act.) passed congress in 2010.
Incidentally, the passage of this law, was not using reconciliation (which requires a simple senate majority) but with 60 votes in the senate.
Article 1, Section 8, Clause 3, of the Constitution known as "the commerce clause" empowers Congress to regulate Commerce.
That is the provision of the U.S. Constitution that gives Congress exclusive power over trade activities among the states.

The term commerce as used in the Constitution means business or commercial exchanges in any and all of its forms between citizens of different states, including purely social communications between citizens of different states by telegraph, telephone, or radio, and the mere passage of persons from one state to another for either business or pleasure.

That law is being challenged on the basis that the federal government has no right to force an American citizen to buy health insurance.
The challenge contends that the decision to not buy HC insurance does not constitute economic activity.

We contend that it does. How?
Because there is a high probability that an American will need a health care provider (Higher probability than having an automobile accident) and when that happens, he/she may not be able to pay:  
            1- Hospitals, Urgent Care centers or Emergency centers, Ambulances
            2- Medications, devices provided to a patient in the E.R. or in the hospital
            3- Services rendered, such as radiology and pathology (heavily involved in interstate commerce)
 In addition,
            4- The institutions providing health care to the uninsured, used construction materials, furniture, and equipment.

All the entities, items, and services mentioned in 1-2-3 and 4 are heavily involved in interstate commerce and that may be affected by the provision of health care to the uninsured.
In addition, It may be point out that individuals decision of not buying health insurance may affect the price others may have to pay for it.
The federal government was trying to solve known problems in the US Health Care system,
high cost, availability (large percentages of uninsured) and quality (Uneven and often poor).

Julio C. Postigo, M.D.