Several times, President Obama has proposed cutting the deduction down to 28% from 35% of mortgage interest payments for Americans in the top income bracket.

But his proposals have gotten nowhere, thanks to lobbying from home builders, the National Association of Realtors and the Mortgage Bankers Association.

But this time, lobbyists are worried. That's because for the first time in years, House Republicans say they are open to scrubbing any tax breaks from the books as part of shrinking federal deficits.

Housing lobbyists have spent a combined $30 million this year, up from $27 million last year, according to Center for Responsive Politics figures.

They're ensuring that leaders don't do anything "penny-wise and pound foolish," said David Stevens, CEO of the Mortgage Bankers Association.

The economy "could actually move backwards" if the deduction is taken away, he warned because it has a significant impact on middle class Americans' cash flow.

Another powerful group, the National Association of Realtors, has spent a record $25 million on lobbying this year, more than any other year, federal records show. The group declined to share its plans on defending the deduction.

But earlier this month, its President Gary Thomas touted that the group had "secured 183 bipartisan cosponsors," this year to support a House resolution that would protect the current tax deduction for mortgage interest.

"We will continue to work with members of Congress on the consumer's behalf on this issue," Thomas said in a statement.