People advocating for and against Gov. Mark Sanford’s tuition tax credit bill have spent about $1 million to influence the General Assembly.

Or they’ve spent millions. Or tens of millions.

We can’t tell you because — but for a few exceptions — they don’t have to tell you. Nor do they have to say who is giving them money.

Many of them don’t want you to know.

But evidence that they’re spending a lot of money is all over South Carolina: Ads for and against the bill are on TV, radio and billboards. Groups have paid for polls, studies, T-shirts, hats, phone trees and slick brochures.

And the groups acknowledge spending about $800,000 on their efforts.

Perhaps not since the Confederate flag has an issue so galvanized the State House.

Some lawmakers say they want to know who is behind it all and think it is time for a change in the disclosure laws.

“This thing has the potential for costing billions of dollars out of the state treasury, and we as legislators should know who’s trying to influence our state,” said Rep. Ted Vick, D-Chesterfield.

Legislative leaders, including House Speaker David Wilkins, R-Greenville, say they might be willing to consider the idea.

“The more openness you have in the process, the better,” Wilkins said. “This may be the genesis for legislation on that.”

Groups interested in bills from video poker to cigarette taxes to civil court changes have tried creative ways to persuade legislators.

However, lawmakers say the tuition tax credit bill, first introduced last year, has attracted unprecedented attention.

While opponents fear tax credits would siphon resources from public schools and other state programs, proponents say the tax credit would push failing public schools to improve.

The groups for and against the tax credit bill say they have the right to keep information about their donors and expenditures secret.

“There is not a 501(c)(3) (nonprofit organization) in the country that discloses its membership list,” said Ed McMullen, president of the S.C. Policy Council, a conservative think tank that has aired ads for tax credits.

When asked by The State for information on its finances, the anti-tax credit group Choose Children First also declined, saying it would put them at a competitive disadvantage.

“We made the decision early on that if the other side is going to (keep it secret) we would not disclose,” said Lee Bussell, of Choose Children First. “It would be unfair to our donors.”

In an election, donations and expenditures by individuals and groups must be disclosed.

But the courts have firmly protected the right of groups in other situations to keep their fund-raising information secret, said John Crangle, executive director of the government watchdog S.C. Common Cause.

“It would be nice if these organizations on their own would disclose their donors,” Crangle said. “It’s a nationwide problem.”

Tax credit opponents speculate that much of the money the bill’s supporters are spending has come from out-of-state groups pushing the proposal.

But supporters of the bill, including South Carolinians for Responsible Government, say most of their money is coming from S.C. residents who want tax credits.

While they wouldn’t fully disclose their own finances, opponents of the bill say lawmakers should be able to know for sure who is trying to influence them.

Out-of-state groups spent tens of thousands of dollars last year — mostly unsuccessfully — to try to get pro-tax credit candidates elected in Richland, Charleston and other counties.

For example, Michigan-based All Children Matter spent $100,000 on advertising against Sen. Joel Lourie, D-Richland, just in the last week before the election.

Tax credit opponents have raised some outside money.

S.C. Education Association president Sheila Gallagher said her organization, which represents teachers, applied for a grant from the National Education Association to fight the bill.

The money has paid for billboards and radio ads criticizing Sanford and the bill. Gallagher declined to say how large the grant was.

The NEA “thought it was a bad bill,” Gallagher said. “They had more questions (about the bill) than we have.”

Whether it’s coming from South Carolinians or outside business interests, lots of money is being spent on the issue.

Lobbying records, which are public, show that the six groups most active in supporting or opposing the bill last year spent, combined, about $200,000 to sway lawmakers.

That is just a fraction of the total money they have spent to influence the outcome of the bill.

The Policy Council has spent $545,000 on advertising, McMullen said, including the cost to produce and air four TV ads. One featured Sanford.

The governor said he was torn over whether groups lobbying the Legislature should be subject to sunshine laws. He said he would have to give it more thought.

The Policy Council also paid for part of an economic study of tax credits. The Illinois-based LEAD Foundation, which lobbies for tax credits nationwide, shared the cost of the study.

Reach Talhelm at (803) 771-8339 or jtalhelm@thestate.com.