MADISON, Wis. — New questions about whether enrollment caps under a statewide expansion of the private school voucher program could be exceeded were raised by Democrats on Thursday as the Senate prepared to pass the state budget.

Under the budget, voucher schools are allowed anywhere in the state but enrollment is capped at 500 students next year and 1,000 students after that. Existing schools in Milwaukee and Racine are not subject to the cap, and they could also enroll students from anywhere in the state without those students counting against the limits.

Democratic Senate Minority Leader Chris Larson said an amendment added to the budget by the Assembly on Wednesday would allow existing voucher schools in Milwaukee and Racine to open satellite schools anywhere in the state that would be outside the enrollment cap.

Whether that could happen would be dependent on how the law is interpreted by state Superintendent Tony Evers, said Bob Lang, director of the nonpartisan Legislative Fiscal Bureau.

Evers is an opponent of expanding the voucher program. Department of Public Instruction spokesman John Johnson said the exact wording of the law would have to be examined.

"We are concerned," Johnson said.

Republican Senate President Mike Ellis, who worked with Gov. Scott Walker on a voucher deal, said he did not believe existing schools could open satellite campuses and enroll students outside the cap.

Republican Senate Majority Leader Scott Fitzgerald said he was unaware of the issue.

"If that's the case, we'd have to address it," he said as the Senate continued budget debate. "But not tonight."

Jim Bender, president of School Choice Wisconsin, said there was never any intent to allow satellite schools to open and it was never a part of any of the discussions that led to the deal.

Bender said he wouldn't oppose fixing it, if there were a question.

The budget must pass the Senate and Assembly in the same form before it can head to Walker for his consideration. Republicans in control of the Senate did not plan to make any changes to what passed the Assembly.

Walker's spokesman did not immediately respond to an email sent after business hours seeking comment.