Several pastors who have publicly backed Huckabee, a Southern Baptist minister who has support from many evangelicals, said they have received the letters, which have no return address. They have arrived in the weeks leading to Thursday's precinct caucuses.
Two letters were sent to the Rev. Brad Sherman, of Solid Rock Christian Church in Coralville. The first arrived a couple weeks ago and warned that he could be prosecuted for his support of Huckabee.
"I just laughed. No one lands in jail for this," Sherman said. "Somebody is trying to intimidate Christians from getting involved."
A second letter came Wednesday. It alleged that the Internal Revenue Service is looking for churches that back candidates in violation of tax rules and mentioned Iowa Sen. Charles Grassley, a Republican who has sought information about spending by high-profile ministries.
The Rev. Kevin Hollinger, of First Baptist Church in Algona, has received three similar letters. Although Hollinger has endorsed Huckabee, he hasn't urged his congregation to support a particular candidate.
"I just encourage people to get out and vote and use their biblical principles," Hollinger said. "I don't tell people who to vote for."
Hollinger said he doubted the letters would intimidate anyone.
The Rev. Rex Deckard has received nine letters, including three on Wednesday.
Deckard, of Calvary Apostolic Church in Des Moines, said he wondered about the motive of the letter writers and assumed they must think pastors are ignorant of the rules regarding church involvement in politics. Regardless, he said the letters won't change his intention of caucusing for Huckabee.
"I'm very impressed with him as a person and I think he's a tremendous individual," Deckard said.
Jim Harris, a Huckabee spokesman in Little Rock, Ark., said the campaign was aware of the letters but did not know how many pastors have received them or whether they were just being sent in Iowa.
"We are gathering more information even as we speak," Harris said. "I would not rule out that we would ask for a criminal investigation, and people who would send such threatening letters to ministers for purely political purposes are cowardly and reek of desperation."
