According to the Romney campaign, the ad will air only in Iowa for now.
It starts out by talking about their similarities as anti-abortion former governors but takes a sharp turn and goes after Huckabee illegal immigration.
Romney campaign spokesman Eric Fehrnstrom tells CBS News' Scott Conroy: "Mitt Romney has a record as governor opposing illegal immigration. Mike Huckabee has a different record of supporting discounted tuition benefits and amnesty for illegal immigrants. We think it's fair to point out those differences."
The ad's script:
MITT ROMNEY: I'm Mitt Romney and I approved this message.
ANNOUNCER: Two former governors…two good family men…
Both pro-life…both support a constitutional amendment protecting traditional marriage…
Mitt Romney stood up, and vetoed in-state tuition for illegal aliens…opposed driver's licenses for illegals.
Mike Huckabee? Supported in-state tuition benefits for illegal immigrants.
Huckabee even supported taxpayer-funded scholarships for illegal aliens.
On immigration, the choice matters.