WASHINGTON -- Republican presidential candidate Rep. Tom Tancredo has demanded that fellow GOP White House hopeful Sen. Sam Brownback apologize for questioning Tancredo's commitment to outlawing abortion.

Tancredo, a congressman from Colorado, and Brownback, a Kansas senator, are vying for support from GOP conservatives who influence the Iowa caucuses.

Brownback's campaign has been making phone calls in Iowa that criticize Tancredo for taking campaign money from a Planned Parenthood backer. It has also posted a press release detailing the accusations.

"Say no to Tom Tancredo and his Planned Parenthood friend and help end abortion in America," the caller says, according to a script confirmed by Brownback's campaign.

"Congressman Tom Tancredo has accepted thousands of dollars in campaign contributions from Dr. John Tanton, a founder of a major Planned Parenthood network," said Brownback's Iowa communications chief John Rankin on the candidate's Web site.

"Federal Election Commission records show that Tancredo's presidential campaign, political action committee, and congressional re-election campaign have accepted thousands of dollars personally from Tanton, and thousands more from a political action committee connected to Tanton," Rankin said.

"Given Tanton's obvious ties to Planned Parenthood, Tom Tancredo should publicly denounce his ties to Tanton and should donate all previously accepted funds to an Iowa crisis pregnancy center," Rankin said.

"How can pro-life Iowans believe Tom Tancredo's commitment to life when he has accepted money from such a prominent abortion supporter?"

Tancredo demanded an apology.

"Sam [Brownback] and I have been friends for several years and he is well aware of my lifelong commitment to the unborn. Yet he has approved the use of despicable and deceitful campaign tactics in an effort to deliberately mislead the voters of Iowa concerning my record and my commitment to life," Tancredo said.

"I call on Sen. Brownback to cease with the maliciously misleading push calls intended to harm me and apologize."

Tancredo's campaign also accused the senator of trying to divert attention away from illegal immigration, Tancredo's main issue. Unlike Tancredo, Brownback has supported giving legal status, under certain conditions, to illegal immigrants.

"Americans from all walks of life, from all racial and religious backgrounds, and from all political persuasions support me because they believe as I do that illegal immigration is the greatest domestic threat we face as a nation and they know I will never resolve this issue by giving amnesty to illegal aliens," Tancredo said.

Tancredo's campaign said the Coloradoan has an "A" rating from the National Right To Life Committee, an abortion opponent.