COLUMBIA - Some Republicans are upset about a letter they say was a threat to get them to support Gov. Mark Sanford's controversial private school tax credit proposal.

The letter and the reaction to it show how the proposal has divided Republicans. The bill would give tax breaks to parents pay for home-schooling their children or sending them to private school.

Tom Swatzel, president of South Carolinians for Responsible Government, sent letters to leaders of national GOP political action committees, warning them that some South Carolina Republicans don't support "school choice."

Swatzel wrote that national Republican groups might regret giving money to those candidates.

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

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.

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 Columbia Republican who opposes the tuition tax credit bill now in the South Carolina House.

Denver Merrill, spokesman for Swatzel's group, said the group wanted South Carolina 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.

"I felt that was uncalled for and irresponsible," said Rep. Adam Taylor, R-Laurens.

Cotty said he's not worried about the group.

"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."

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 take money from public schools.