ABC News' Shushannah Walshe and Michael Falcone report:

DAVENPORT, Iowa - An Iowa Christian conservative leader who bestowed his highly sought-after endorsement on presidential candidate Rick Santorum this week is now at the center of a controversy over whether he asked for cash in exchange for his public support.

Less than 48-hours after receiving the backing of Bob Vander Plaats, the head of the prominent evangelical group The Family Leader, Santorum disclosed that the prominent Iowan told him he needed money to make the most out of the endorsement.

And sources familiar with talks between the conservative heavyweight and representatives from several of the Republican presidential campaigns went a step further, describing Vander Plaats' tactics as corrupt.

"Clearly the endorsement was for sale - without a doubt," one source said.

It's a charge that The Family Leader flatly denied.

"The allegation by an unnamed source that Bob Vander Plaats asked any campaigns for money in exchange for his endorsement is absolutely false," according to a statement issued by the organization on Thursday. The Family Leader said Vander Plaats was unavailable for an interview Thursday.

But even Santorum acknowledged in an interview with CNN that money was among the topics he and Vander Plaats discussed last weekend ahead of Tuesday's endorsement press conference.

"What he talked about was he needed money to promote the endorsement and that that would be important to do that," Santorum told CNN. "There was never a direct ask for me to go out and raise money for it."

The former Pennsylvania senator's statement differs from what he told ABC News on Monday night - just hours before Vander Plaats endorsed him. At a campaign event in Indianola, Iowa, Santorum said the issue of money never came up in his conversations with the Christian leader.

In a statement Santorum's National Communications Director Hogan Gidley said, "I don't know about the discussions other campaigns had, but we did not, nor would we ever agree to raise a single penny for another entity. We're focused on our own campaign and that's where our resources will be spent."

Though Santorum did not specify the dollar amount he and Vander Plaats discussed, multiple sources said he was soliciting as much as $1 million from Santorum and other candidates.

In an interview with the Des Moines Register this week, Vander Plaats said that it was his "ethical responsibility" to essentially put some money where his mouth is.

"You can't say, 'We endorsed you. Now see you later,'" Vander Plaats told the Iowa newspaper. "That's not going to do a lot in the long run."

But one long-time Iowa conservative activist told ABC News, "There is no way he could buy enough ad space in Iowa for a million dollars - couldn't buy that much advertising in a week and a half in Iowa."

ABC News has learned that Vander Plaats tried to solicit money for his endorsement during the last presidential cycle too. A former staffer for Mitt Romney's 2008 presidential bid who is currently unaffiliated with a campaign said Vander Plaats came to them seeking money for his backing if he supported the former Massachusetts governor.

"He wanted to be paid," the former staffer said. "He was clearly looking for a paycheck. There was a conversation about him getting a title, but being a paid consultant was much more important."

The aide said they offered him a title, but never seriously considered paying Vander Plaats. He ended up endorsing Former Arkansas Gov. Mike Huckabee over Romney.

Unlike four years ago, when members of Iowa's evangelical community helped then-candidate Huckabee to a first place finish in the caucuses, no candidate appears to be drawing the same kind of support from the important group of voters.

A well-known conservative figure in the state that ran unsuccessfully for governor in 2010, Vander Plaats' endorsement had been seen as a key indicator of social conservative sentiment.

At a press conference in Urbandale, Iowa on Tuesday, Vander Plaats called Santorum, "the Huckabee in this race."

"I saw him as a champion for the family in the U.S. House, I saw him as a champion for the family in the U.S. Senate. I saw him as a champion for the family on the campaign trail," he said. "I believe Rick Santorum comes from us, just not to us, he comes from us."

Though Thursday's statement from The Family Leader noted the group's board was "was unanimous in their personal support for Rick Santorum," there was no organization-wide endorsement. Instead, Vander Plaats and another Family Leader official Chuck Hurly, both publicly backed Santorum.

But Vander Plaats tried to exert his influence in other ways, suggesting to Michele Bachmann combine forces with another candidate in order to make it easier for social conservatives to rally behind one candidate ahead of Iowa's Jan. 3 caucuses.

"After much prayer and discernment, The Family Leader board members directed Bob to contact Rick Perry, Michele Bachmann, and Rick Santorum to present the concept of merging in order to provide a solution to the fractured vote of caucus-going conservatives," according to the group's statement. "At no time did Mr. Vander Plaats make any specific demands in regard to who should merge with whom."

Bachmann did not take him up on the offer. She has separately won the backing of the former head of The Family Leader as well as more than 100 Iowa pastors.

ABC's Arlette Saenz contributed to this report.