Zubik vs. Burwell is the Supreme Court's name for the set of cases more often identified with the Little Sisters of the Poor, a religious order that is also a party to the case. I filed an amicus brief in Zubik on behalf of the Baptist Joint Committee for Religious Liberty. I had never before filed a brief in support of the government in a case about the free exercise of religion.

The facts in this case, which are scheduled to be argued Wednesday, are complicated. The Affordable Care Act requires insurance plans to cover contraception without imposing deductibles or requiring co-payments. But Catholic institutions object to providing contraception, and many conservatives of other faiths object to providing emergency contraception, which they plausibly view as sometimes causing very early abortions.

The government responded to these concerns in two ways. Churches and their integrated auxiliaries — the religious organizations most closely integrated with the church itself — are exempt. What's more, their insurance companies are exempt. The regulation carefully exempts these employers and, in a second clause, exempts any "health insurance coverage" provided "in connection with" their health plans.

All other conscientious objectors are also exempt, but their insurance companies are not. If an employer refuses for religious reasons to cover contraception, the government instructs the employer's insurance company to provide free contraception separately, with segregated funds and segregated communications to employees, and to explain to the workers that the employer refuses to provide it.

Many religious organizations accepted this solution, but some did not. The remaining objectors make two claims. First, they say they cannot in good conscience provide the government with contact information for their insurers. There is nothing confidential or religious about that information, but they maintain that providing it to the government is a necessary step for the eventual delivery of contraception.

Second, they say that the insurance company will use the "infrastructure" of the employer's insurance plan to deliver contraception. In practical terms, this appears to mean their employees' names and addresses. More conceptually, the objectors say the government is using their insurance plans.

The objectors would make this second objection even if the government had put the obligation on insurers from the beginning, so that no one had to provide it with contact information, and even if employers were not required to provide insurance at all. Even if employers were required to do absolutely nothing, the insurance companies would still use the "infrastructure" of any insurance plan that the employers voluntarily offered to their workers.

So their real objection is to what their secular insurers are required to do. The religious objectors demand a right to control how the government regulates insurance companies.

To support this claim, they make two arguments that actually endanger religious liberty. First, they say that only they can say what is a substantial burden on their exercise of religion; the courts must take their word for it. But that would give rise to even more extreme claims and discredit the cause of religious liberty.

These organizations say they cannot contract with any insurer that provides contraception to their employees. Another group might say it cannot contract with any insurer that provides contraception to anybody at all. Or suppose someone says he cannot in conscience obey the laws of any government that permits abortions.

On the Zubik plaintiffs' theory, courts could not question any of these claims. A finding that a law imposes a substantial burden on religion would become automatic; the only issue in any case would be whether imposing that burden serves a compelling government interest by the least-restrictive means.

Only the believer can say what is a substantial burden religiously. But courts must say what is a substantial burden legally. Believers should get substantial deference on that question, but they cannot get absolute deference, and they never have. Courts decide the cases and set the outer boundaries.

The second, and even more dangerous argument: These organizations say that because the government exempted the insurers of churches and their integrated auxiliaries, it is required to exempt the insurers of all other conscientious objectors as well. Otherwise, it discriminates between two groups of religious organizations.

This argument is a mortal threat to an essential and widespread source of protection for religious liberty. There are thousands of specific religious exemptions in U.S. law. If legislators and administrative agencies cannot enact a narrow religious exemption without it being expanded to become all-inclusive, many of them will not enact any religious exemptions at all. And they will start repealing the exemptions they have already enacted.

These arguments may offer the best chance to win this one case, but they would do terrible damage to the larger cause of religious liberty, which is already unpopular on the left. A ruling for these religious plaintiffs would make it much, much worse.

Douglas Laycock is a law professor at the University of Virginia. He wrote this article for the Washington Post.