Money issues already prompted House Republican budget-writers to scale back the proposal that would've opened the program up to thousands of more students by waiving the one-year public school requirement for current private school students.
Democrats maintain it's irresponsible to expand the program when it is only in its second year and a lawsuit challenging it is awaiting a ruling from the state Supreme Court.
Challenges that advocates of expanding voucher eligibility might face in the Republican-dominated Senate, however, are the cost and questions of whether the Legislature should start making exceptions to the 2011 compromise that then-Gov. Mitch Daniels touted as giving public schools a chance to win over students and parents.
Senate Appropriations Committee Chairman Luke Kenley, R-Noblesville, said he was hesitant to back the voucher expansion for both reasons.
"I think we struck a bargain there a couple years ago," Kenley said. "I think we need to let it work four or five years before we start monkeying with it too much."
The Senate education committee is scheduled to have a public hearing Wednesday on the proposal that's being backed by Republican Gov. Mike Pence, with a committee vote possible the following week.
The committee's chairman, Republican Sen. Dennis Kruse of Auburn, said he saw some merit to having the public school requirement, but was open to the bill's exceptions for siblings of current voucher students, children in military and foster families and for children with special needs.
"I think there's a better case for that," Kruse said. "The kindergarteners are a bigger change in that policy."
About 9,100 Indiana students are receiving vouchers averaging nearly $4,100 each this school year. The House Republican budget proposal forecasts spending for the voucher program to grow over the next two years from the current $37 million a year to $63 million annually, with the number of students growing to 15,000 in the 2014-2015 school year.
A report by the nonpartisan Legislative Services Agency said it couldn't determine an estimate on the cost of the proposed voucher expansion, but that it "is likely to be significant."
The state Supreme Court is weighing the legality of the program after hearing arguments in November over a lawsuit pressed by the Indiana State Teachers Association that virtually all of the voucher money goes to schools whose primary purpose is to promote the teachings of their affiliated churches.
Voucher supporter Sen. Doug Eckerty, R-Yorktown, said he believed the bill's provisions for expanded eligibility are the "logical next moves" to allow low-income families more options in the education of their children.
Eckerty said he wasn't convinced the expansion would cost the state that much because private schools have a limited number of additional students they can accept.
"I'm not expecting any big expansion of private school seats," Eckerty said. "I just don't think we're going to have it."
Lindsey Brown, executive director of School Choice Indiana, said the group had sought an elimination of the public school requirement but understood the state's financial concerns about doing so this year.
Brown said while the vast majority of Indiana's more than 1 million students will remain in public schools, she didn't believe that low-income families should have their options limited by the current law that makes their children unable to receive vouchers before 2nd grade.
"They shouldn't be forced to attend a school that may or may not meet their needs for two years until they can become eligible for the program," Brown said.
The prospect of loosening the voucher eligibility rules raises worries about where the number of students in it will peak, said Sen. Tim Skinner, D-Terre Haute.
"The more quickly it grows, then the more quickly money is being drawn from the public school system and something's gotta give," said Skinner, a retired teacher from West Vigo High School.
Kenley, the Appropriations Committee chairman, is also a member of the Senate education committee and said the question of broadening the eligibility rules loomed large for him going into next week's bill hearing.
"I'll listen to what they have to say," he said. "But I'm not sure I feel it's justifiable to make that change."