Perry and the former Massachusetts governor are considered the front-runners for the GOP presidential nomination. Romney has been criticizing Perry repeatedly on the in-state tuition issue, which is disliked by many conservatives.
The issue gained traction when Perry discussed his position at the Fox News/Google debate in Florida last week and said those that disagree don't "have a heart."
"If you say that we should not educate children who have come into our state for no other reason than they have been brought there by no fault of their own, I don't think you have a heart," said Perry during the debate, which is shown as a clip in the Romney ad.
Perry said Wednesday his heartless remark was "inappropriate" and he was "probably a bit over-passionate," but stood by his position.
"In Texas in 2001 we had 181 members of the legislature — only four voted against this piece of legislation — because it wasn’t about immigration it was about education," Perry said in the interview with Newsmax.