Former House Speaker Newt Gingrich said Monday he was unaware of House rules prohibiting lawmakers from using their taxpayer-paid franking allowance to sent out Christmas mailings.

"This is actually weird," he said at a campaign event in Davenport, Iowa. "I am told -- I've been investigating this for the last three days -- I am told that this is actually a 20 or 30-year-old law which I have to say I find strange, and I would advocate repealing the law."

"Apparently if the president sends out Christmas cards, they are paid for the Democratic or Republican National Committees because no federal official at any level is currently allowed to say 'Merry Christmas.' And the idea, I think, is that the government should be neutral. I'm going to go back and find out how was this law written, when was it passed. We've had this whole -- in my mind -- very destructive attitude in the last 50 years that we have to drive religion out of public life."

The Washington Examiner first reported that holiday greetings could not be franked. Birthday, anniversary, wedding, birth, retirement or condolence messages are also prohibited.

Franked mail includes unsolicited mass-mailings such as newsletters and meeting notices that members of Congress send their constituents at taxpayers' expense.

Watch this video from CNN, broadcast Dec. 19, 2011.

With reporting by David Edwards