"Christ would not vote for Barack Obama because Barack Obama has voted to behave in a way that it is inconceivable for Christ to have behaved," Keyes said. He referred to Obama's votes against anti-abortion legislation.
Keyes has made opposition to abortion the centerpiece of his campaign. His choice of words on gay marriage and abortion has stunned Illinois Republican Party leaders.
On Tuesday, Keyes complained about a remark Obama made while campaigning downstate.
"I don't want to just win, I want to give this guy who is running against me a spanking," Obama said of Keyes.
Keyes asserted that Obama's use of the word spanking was "the language of the master who, when he is displeased with the slave, gives him a whipping."
Both men are black.
Julian Green, a spokesman for Obama, acknowledged that Obama made the comment but said assertions that they were racist "are just wildly ridiculous."
"Anyone who reads this tongue-in-cheek quote will clearly understand that Barack Obama wants to win this race and represent the working families of Illinois. No one has run a more hopeful and positive campaign than Barack Obama," Green said.
Keyes also brought up race last month when he compared Obama's views on abortion to "the slaveholder's position."