It's an issue that has dogged Obama since his days in the Illinois State Senate.
The Born Alive Infant Protection Act would have required medical attention for infants born alive during an attempted abortion. Obama voted against it more than once. Why?
Click play to get more insight from CBN News Political Reporter David Brody, as well as more on born-alive infants from failed abortions from Jill Stanek with Born Alive Truth.
Obama says to protect Roe v. Wade and keep abortion legal. But even most abortion rights supporters say Roe wasn't at risk.
The National Right to Life Committee says Obama keeps changing his reasons for opposing the bill.
"We believe that he should come clean and admit that he has misrepresented his vote in the past on this Born Alive Infant Protection Act and that he should apologize to those that he has called liars," said Susan T. Muskett with the National Right to Life Committee.
Indeed, in an exclusive interview with CBN, Obama had harsh words for those questioning his position and vote.
"I hate to say that people are lying, but here's a situation where folks are lying," Obama told CBN News.
Let's rewind to 2000. A federal version of the Born Alive bill is introduced but defeated. Two years later, pro-choice lawmakers finally support the bill because wording was added that protected the legality of Roe v. Wade.
The same fight was going on in Illinois at the state level. There, state senator Obama voted against all Illinois versions saying they were different than the law passed by Congress - because they didn't protect Roe sufficiently under Illinois law.
"I would have been completely in, fully in support of the federal bill that everybody supported, which was to say that you should provide assistance to any infant that was born -- even if it was as a consequence of an induced abortion. That was not the bill that was presented at the state level," Obama said.
Read more on the Born Alive Infant Protection Act by clicking here
That is where National Right to Life makes its case. It has produced a document showing that the same language protecting Roe was indeed in a 2003 version of the Illinois bill. Yet Obama, the chairman of the committee responsible for the bill, still voted against it.
The Right to Life Committee believes this discrepancy is part of a bigger issue.
"I think the American people need to know how extreme he is and the role that he played on this," Muskett said.
In a statement to CBN News, the Obama campaign wouldn't address the charge that he's misrepresented his position on this bill. They don't believe it's necessary since there were multiple versions of the bill at different times.
Instead they told CBN "the suggestion that Obama - the proud father of two little girls - and others who opposed these bills supported infanticide is deeply offensive and insulting ... the bills Senator Obama voted against in Illinois were crafted to undermine Roe v. Wade or pre-existing Illinois state law."