Republican lawmakers are outraged at a letter they say was a threat to get them to back Gov. Mark Sanford’s controversial private school tax credit proposal.

The letter — and the reaction to it — show how heated the debate over the tax credit bill has become among Republicans.

House Republicans are divided over the bill, which would give tax breaks to parents who want to home-school their children or send them to private school or another public school.

Several GOP lawmakers were furious when they opened their mail last month and found copies of a letter from a group advocating the tax credits.

Tom Swatzel, president of South Carolinians for Responsible Government, sent letters to leaders of national GOP political action committees, warning them that some S.C. Republicans don’t support “school choice.” If national Republican groups give money to those candidates, they might later regret it, Swatzel wrote.

A copy of the letter sent to one GOP group — U.S. Senate Majority Leader Bill Frist’s Volunteer PAC — also went to every House Republican.

“They lose their legitimacy when they do things like that,” said state Rep. Dan Cooper, R-Anderson.

Swatzel’s letter said the PAC organized by former U.S. Rep. John Kasich, R-Ohio, “unfortunately donated $1,000 to State Representative Bill Cotty,” a Richland Republican who opposes the tuition tax credit bill now in the S.C. House.

“When you make a donation,” the letter reads, “it is important that you know whether ... (the candidate) is actively working to undercut these positions.”

Denver Merrill, spokesman for Swatzel’s group, said the group wanted S.C. lawmakers to know PACs were investigating who supports the tuition tax credits.

But some Republicans took the letter as a threat that the group would try to prevent them from getting campaign contributions if they didn’t get behind the bill.

They also were offended that the group singled out Cotty, whom many respect for his independent-mindedness.

“I felt that was uncalled for and irresponsible,” said Rep. Adam Taylor, R-Laurens, who said the letter came without explanation.

The House is scheduled to debate the bill later this month.

Supporters say the measure would give parents more options and push public schools to improve.

Opponents say the tax break would blow a hole in the state budget, making it hard to pay not only for public schools, but also for programs from the highway patrol to mental health care.

Swatzel’s letter angered supporters of the bill, too.

“Believe me when I say that engaging opponents in a personal manner has far more potential to cause problems for the legislation,” House Majority Leader Jim Merrill wrote in a letter to Swatzel.

Jim Merrill is Denver Merrill’s brother and a tax credit supporter.

Cotty, a former Richland 2 school board member, said he is not worried about South Carolinians for Responsible Government.

“In my district, if my biggest fault is that I’m an outspoken advocate of public education,” he said, “I can tell you what you can call me — re-elected.”

Cathy Hazelwood, general counsel for the S.C. Ethics Commission, said letters that imply a group might try to interfere in a candidate’s fund raising do not break ethics laws.

“It’s a threat,” she said, “but it’s not a bribe.”

A spokesman for Frist said no one in his PAC office had seen the letter.

Several lawmakers say they support school choice — just not the bill as written. A number say they would support testing the program in a few counties.

Denver Merrill said it is up to individual lawmakers to explain their positions to the PACs.

South Carolinians for Responsible Government did write a letter back to House Republicans apologizing for naming Cotty in the letter to the PACs, Denver Merrill said, but stood by the letter.

“There’s no threat involved,” he said. “It was a letter meant to convey ... that we suggest (PACs) research who they contribute to.”

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