Their tax-exempt ministries take in millions and now Iowa Sen. Charles Grassley, the top Republican on the Senate Finance Committee, is asking whether these churches really are non-profits.
Georgia megachurch pastor Creflo Dollar is one of the televangelists who was asked to provide financial information.
"We don't have any problems complying to a valid request," Dollar told CBS News' The Early Show co-anchor Julie Chen.
But he questioned whether it was appropriate for the Senate Finance Committee "to become a tax examiner and to get involved in the information of private, nonprofit organizations when the IRS has already been assigned that responsibility."
Asked about some specific assertions by Grassley, Dollar denied that two Rolls-Royces were purchased by the church for him and his wife.
"That's not true. First of all, we don't have two Rolls-Royces," he said. "And secondly, the one Rolls-Royce that was purchased was purchased by the donors, or the members of the church, and it was a surprise to me. I had no idea they were doing it."
Dollar also responded to claims that he tried to raise $1 million from other ministries to give to fellow evangelists Kenneth and Gloria Copeland to celebrate their anniversary, and that his ministry gave over half a million dollars.
"Also not true," Dollar said. "We didn't give Kenneth $500,000, and we didn't take it from our church. We sent letters to different ministers around the country inviting them to share in honoring Kenneth Copeland's 40th anniversary. It's an opportunity for people to do what they believe, and unless we completely got rid of the First Amendment, that's our opportunity to believe that we can sow into a man of God's life, be a blessing to him and celebrate his 40 years of service in the ministry."
Asked whether there are televangelists who abuse the faith of believers and misuse church funds, Dollar said, "There are some bad apples out there. But we've got to make sure that in our fear to try to locate those bad apples that we don't put everybody in that same bucket and automatically assume because of that fear that everybody is the same."
Others under scrutiny include Copeland, faith healer Benny Hinn and one of the nation's best known female preachers, Joyce Meyer.
Grassley sent letters to a half-dozen Christian media ministries earlier this week requesting answers by Dec. 6 about their expenses, executive compensation and amenities, including use of fancy cars and private jets.
In a statement, Grassley said he was acting on complaints from the public and news coverage of the organizations.
"The allegations involve governing boards that aren't independent and allow generous salaries and housing allowances and amenities such as private jets and Rolls-Royces," Grassley said.
"I don't want to conclude that there's a problem, but I have an obligation to donors and the taxpayers to find out more. People who donated should have their money spent as intended and in adherence with the tax code."
Those ministries that responded Tuesday either said they were cooperating or committed to financial transparency and following the law.
The investigation promises to shine new light on the kind of TV ministries that were crippled by sex and money scandals in the 1980s. Experts also say it stands out as an unusual case of the government probing the inner workings of religious organizations.
Most of those under investigation preach a variation of the "prosperity gospel," the teaching that God will shower faithful followers with material riches.