INDIANAPOLIS (AP) — Teachers, administrators and clergy sued Friday to block the nation's broadest private school voucher plan on the day it took effect, arguing that the new Indiana law violates state constitutional provisions on education and protecting taxpayers from supporting religious institutions.

An advocacy group experienced in defending voucher plans across the country quickly said it would back the new law in court and seek to intervene on behalf of parents who could benefit. Gov. Mitch Daniels, Superintendent of Public Instruction Tony Bennett and other state officials issued statements supporting the law, which for now allows a limited number of low- and middle-income families to use public money toward private school tuition. The program eventually will be open to nearly two-thirds of the state's families.

The lawsuit filed in Marion County seeks a preliminary injunction on grounds that most of the 352 private schools whose students are eligible for the vouchers are affiliated with churches or other religious institutions. It also said the Indiana Constitution directs the General Assembly to educate children through a "general and uniform system of Common Schools."

"This voucher program will provide public funds to private schools that can give individual preference to students based on test scores, disabilities, wealth and personal faith. Such preferences should not be publicly funded," said lead plaintiff Teresa Meredith, a Shelbyville public school teacher and vice president of the Indiana State Teachers Association, the state's largest teachers union.

The new law could cut funding to public schools by up to $65.8 million, according to the ISTA.

"The implementation of this law will most certainly result in larger class sizes, more teacher layoffs and fewer instructional programs for Hoosier public school students," Meredith said.

At least two of the other 11 plaintiffs also are affiliated with teachers unions. They include a public school superintendent and former state school board member, a public school principal, and Methodist and Baptist ministers.

Named as defendants are Daniels and Bennett, who both strongly supported the voucher law as part of sweeping school changes approved by the Republican-dominated General Assembly this year. Daniels signed the plan into law May 5.

"There the union goes again, putting their financial self-interest ahead of the interests of children and Indiana's low-income families," Daniels said in a statement. "The bill was drafted from its inception with the state and federal constitutional law in mind."

The Institute for Justice, an Arlington, Va.-based school-choice advocacy group, said it would seek to intervene in the case on behalf of a group of Indiana families who wish to receive vouchers. Vouchers are government-issued certificates that can be applied to private-school tuition, essentially allowing parents to redirect some of the tax dollars that would normally go to public schools.

"We have parents that are very interested in taking advantage of the program," Bert Gall, an Institute attorney, said in a telephone interview Friday. "They believe educational opportunity is important not only for their children but for children throughout the state of Indiana."

Indiana's voucher plan "shares basically the same characteristics" as plans in Milwaukee and Cleveland that the Institute has successfully defended in court, Gall said. He said plaintiffs in the complaint filed Friday were mistaken in arguing that the state would be giving aid directly to private schools affiliated with a religion.

"It's the state giving aid to students and parents, and it's the parents deciding how they want to use that aid," Gall said.

Indiana House Speaker Brian Bosma, R-Indianapolis and co-author of the voucher legislation, said such programs have proved successful in other states and "in order to compete in the 21st century, we must offer every Hoosier family the educational opportunities that best meet their needs."

Students receiving vouchers make up less than 1 percent of school enrollment nationwide, but vouchers have been one of the top priorities among conservatives.

Indiana's program will be limited to 7,500 students this coming school year and 15,000 next year, but then there will be no limit on the number of children who could enroll as long as their parents fall within income limits. Families of four currently earning up to about $60,000 a year could receive them.

The actual value of the vouchers would be based on a sliding scale and would be less than the amount of tax money a public school would have received for that student. The maximum value for students in first through eighth grade would be $4,500.

The lawsuit's 12 plaintiffs are from Indianapolis, Evansville, Lafayette and Shelbyville, and include Edward Eiler, a Lafayette school superintendent and former member of the Indiana State Board of Education, and retired Methodist minister Richard Hamilton, the father of federal appeals judge David Hamilton.