Rick Santorum (AP)

Rick Santorum faces new criticism Monday morning after a heated exchange with a New York Times reporter, who asked the GOP presidential hopeful about a remark he made about opponent Mitt Romney.

Santorum referred to Romney in a speech Sunday as "the worst Republican in the country to put up against Barack Obama."

When asked to clarify his statement afterward, Santorum lashed out, telling NYT reporter Jeff Zeleny to "stop lying" in a testy back-and-forth between the two.

"What speech did you listen to?" Santorum asked when pressed to explain what he meant by his attack on Romney.

"This one," Zeleny replied, to which Santorum told him to quit lying.

Santorum continued his tirade.

"I didn't say that. You guys are distorting what I'm saying...quit distorting my words. It's (expletive)."

Santorum said Monday that the exchange was just par for the course.

"If you haven't cursed out a New York Times reporter during the course of the campaign, you're not really a real Republican's the way I look at it. It was just one of these harassing moments, and after having answered the question a few times, sort of comes back with the same old fashion, the same old spin," he said on Fox News.

"I just said 'Okay, I've had enough of this you-know-what."

Santorum's team have turned the comments into a campaigning tool, sending out an e-mail to supporters asking for a $30 contribution, what they say is the price of a NYT subscription.

""I criticized Romney and Obama for their outrageous healthcare legislation. Predictably, I was aggressively attacked by a New York Times reporter all too ready to defend the two of them, and all too ready to distort my words," Santorum wrote in the email. "Let me assure you, I didn't back down, and I didn't let him bully me."

Zeleny says Santorum was playing to the cameras.

"It's a very common tactic for Republican presidential candidates. Or even Democratic presidential candidates to try and use the media a foil here. We've seen Newt Gingrich do it throughout the campaign season.

"He clearly knew the cameras were rolling here."