Sen. Barack Obama has unleashed a new attack on John McCain's stance on abortion, saying he will "take away [women's] right to choose."

The Obama campaign released the radio last Thursday, before McCain's Palin pick, and it has been airing in several swing states. Politico.com readers in Florida, Virginia, Iowa, Ohio, Indiana, Wisconsin and Colorado all said they had heard the ad. One man commented that it had been played at least 12 times in one day.

A female nurse practitioner narrates the ad, which includes has excerpts of McCain's comments on abortion.

"If Roe vs. Wade is overturned, the lives and health of women will be put at risk. That's why this election is so important," the woman said. "John McCain's out of touch with women today. McCain wants to take away our right to choose. That's what women need to understand. That's how high the stakes are."

McCain aides didn't respond to the ad, but Republican Party communications director Danny Diaz chimed in.

"[Obama] has offered misleading statements on the issue and is now trying to confuse voters by attacking Sen. McCain," Diaz said.

Some analyst believe John McCain's decision to make Gov. Sarah Palin his running mate was largely about taking Hilary Clinton supporters away from his opponent.

Obama spokesman Bill Burton confirmed the ad was sent to stations before McCain's choice was made public, and that it had nothing to do with its contents.

"This is a straightforward ad about the very well-documented fact that he wants to overturn Roe vs. Wade and supports a constitutional ban on abortions," he said.