Striking down Indiana's school voucher program because some schools are affiliated with churches would amount to unnecessary government interference into religion, the law's supporters argue in court documents.

Opponents led by the Indiana State Teachers Association want the Indiana Supreme Court to overturn the voucher law, which has been upheld by a lower court. Indiana's voucher program is the largest in the nation, with nearly 4,000 students participating. Opponents claim the program violates a state constitutional ban on government support of churches because it compels taxpayers to pay for schools that teach religion.

The Indiana attorney general's office and other groups defending the law argue in court briefs filed last week that nobody is being compelled because parents are free to send their children to any school they want — public, private or parochial.

"These programs were not created for the benefit of religious schools or institutions, but for the benefit of students, and only through their choices do taxpayer funds arrive at religious schools," state lawyers argue in their 50-page brief.

Opponents are essentially claiming that parochial schools — which account for the majority of private schools in the program — shouldn't receive scholarship money because they are "pervasively sectarian," supporters say. Supporters say judging the law's constitutionality based on the religiosity of some schools requires the court to determine how religious various schools are, which in itself is unconstitutional.

"It calls for an inquiry into — and a subjective judgment about — each school's religiosity that is fraught with peril under the First Amendment," attorneys for the Virginia-based Institute for Justice said in their brief filed on behalf of two parents. Groups including the Council of Christian Colleges and Universities, the Beckett Fund for Religious Liberty, and the Friedman Foundation for Educational Choice also filed friend of the court briefs.

John West, the Washington attorney handling the court challenge, said he would reserve any comment on supporters' arguments for his own brief, which is due April 30.

A private attorney who has taught and lectured on the Indiana Constitution said supporters' argument was novel.

"They're using an argument that's usually used against state support of religion," said Jon Laramore of the Indianapolis law firm of Faegre Baker Daniels. "But here they're posing the argument that if government has to decide which schools have too much religion to get vouchers, that in itself will violate the rule against too much state entwining in religious organizations."

Marion County Judge Michael Keele found in his January order upholding the law that whether or not some schools were religious was irrelevant, because parents had the choice of which school their child should attend.

The attorney general's office is asking the state Supreme Court to uphold Keele's ruling.

The larger argument — that the scholarships aren't state support of religion because parents make the choice of where to spend the money — is similar to arguments that have been used in federal court cases that have upheld vouchers, Laramore said. But that didn't necessarily mean Indiana would follow suit, he said.

"The Indiana Constitution is much more specific in its language prohibiting state financial assistance to religious institutions, so it is not clear that Indiana courts would reach the same conclusion that federal courts have reached," Laramore said Thursday.

An attorney for the Institute of Justice, which is defending the law, said barring parochial schools from receiving scholarships would also deprive parents and students of their religious rights.

"Taking away an option because of its religiosity in a program like this is impermissible discrimination both against the provider of the option and its recipient," Bert Gall said in an email to The Associated Press.

Opponents also claim that the program unconstitutionally takes funds from public schools and sends the money to private schools. The state and other supporters say striking the law down on that basis would endanger other public scholarship programs that send students to private or religious colleges.