By BETSY MCCAUGHEY

Eighteen states are challenging the constitutionality of the Obama health law. Their challenge focuses on whether the federal government can require everyone to buy coverage. They gloss over an issue more consequential to our health and longevity: Can the federal government dictate how doctors treat their patients?

During the last half century, the Supreme Court has established a zone of privacy protected by the Constitution. It includes a couple’s choice to use contraception recommended by their physician (Griswold v. Connecticut, 1965) and a woman’s choice to have an abortion provided by her physician (Roe v. Wade, 1973). How can freedom to make these choices with your doctor be protected and not freedom to choose a hip replacement or a Caesarean section? Either your bodyis protected from government interference or it’s not.

The Obama health law requires that nearly everyone enroll in a “qualified” plan, then says plans can pay only doctors who implement whatever regulations the Secretary of Health and Human Services imposes to improve health-care “quality” (Section 1311). That covers everything in medicine. Never has the federal government dictated how doctors treat privately insured patients, except on narrow issues such as drug safety. If challenged, this provision is likely to meet disapproval from a pro-privacy court.

The new health law is defended on the basis of the Congress’s power to regulate interstate commerce. While the Supreme Court has stretched the meaning of interstate commerce to justify congressional lawmaking in many areas, the definition is not boundless.

Some members of Congress hoped that the Court’s ruling in Gonzalez v. Raich (2005) would give them a constitutional EZ Pass to control health care. In that case, the Supreme Court ruled that federal agents had the authority to stop Angel Raich from consuming home grown marijuana for medical purposes, though it was permitted in her state and advised by her doctor. Amazingly, the Court said her homegrown supply—six stalks in all—could have “a substantial effect on supply and demand in the national market for that commodity.”

In September 2005 Sen. Patrick Leahy (D., Vt.) grilled John Roberts, then the nominee for Chief Justice, demanding assurances that he would stand by the Raich ruling instead of trying to restrain congressional lawmaking on health care. The surprise came in the Supreme Court’s next term, when in the words of Justice Clarence Thomas, the Court made a “hasty retreat” from Raich.

Oregon had passed a Death with Dignity Act setting standards for doctors to administer lethal drugs to terminally ill patients who requested them. The Bush administration argued that assisted suicide was not “legitimate” medical care, and therefore federal agents could halt the use of the drugs.

The Supreme Court ruled 6-3 against the Bush administration’s interference in Gonzales v. Oregon (2006). Such intrusion, the court said, “would affect a radical shift of authority from the States to the Federal Government to define general standards of medical practice in every locality.” That’s what the Obama health law does.

For example, it requires doctors to record patients’ treatments in an electronic medical database and monitors doctors’ decisions. Dr. David Blumenthal, the Obama administration’s National Coordinator of Health Information Technology, explained in the New England Journal of Medicine last April that “embedded clinical decision support”—his euphemism for computers telling doctors what to do—will manage the quality of doctors’ decisions. The Supreme Court is likely to view these controls as a “radical shift” in authority from the states to the federal government, and even more important, a threat to privacy rights.

Before the current health debate, the public discussed government interference in medical decisions largely in one context: abortion. When a lower federal court struck down the Partial-Birth Abortion Ban Act in 2004 (a decision later reversed by the Supreme Court), Planned Parenthood of Los Angeles CEO Mary Jane Wagle said “this ruling is a critical step toward ensuring that women and doctors—not politicians—make private, personal health care decisions.” During the litigation, federal authorities requested access to medical records to determine whether the partial birth procedure was ever medically necessary. Privacy advocates defeated nearly every request.

Advocates for women’s rights need to reassess the impact of the new health law. Whether you are a man or a woman, pro-choice or pro-life, you lose freedom and privacy under this law.

Ms. McCaughey is the author of two books on the writing of the U.S. Constitution and a former Lt. Governor of New York.