Zillow.com already competes against Google in the online real estate listings business. Now, the Seattle startup may face additional competition from the Internet search titan around mortgages.

The New York Times reports that Google plans to begin offering mortgage quotes as early as this month, citing a lawsuit from potential competitor LendingTree. The suit was filed in U.S. District in North Carolina against Mortech, a Lincoln, Nebraska technology provider that works with LendingTree.

It says that Mortech plans to offer its pricing engine services to Google as part of the company's move into the mortgage quote business, a move that LendingTree claims violates the terms of its contract with Mortech. The suit does not mention Zillow, but I have an email into the company to see if they work with Mortech.

The suit -- full copy of which can be found here --  says:

LendingTree recently learned that Google imminently plans to launch a loan aggregation service in late August or early September of this year that would compete directly with LendingTree. LendingTree has also learned that Mortech intends to make its pricing engine services available for use with Google’s new service and will send information related to mortgage loan offers to be displayed to consumers on Google’s website.

Zillow.com launched its free Mortgage Marketplace in April 2008 at the time saying that the product would offer "borrowers an anonymous and hassle-free way to request custom loan quotes directly from registered lenders."

As mortgage rates fell earlier this year, the Zillow marketplace attracted home owners who used it as a tool to research to decide whether to refinance. That, in turn, helped drive record traffic to the Web site.

Obviously, having Google in the mix would be problematic -- as guest writer Galen Ward noted in a column for TechFlash earlier this month.

UPDATE: Spencer Rascoff, chief operating officer at Zillow, said that they have not yet seen the LendingTree lawsuit and therefore he couldn't comment on it. However, he said that Zillow is not party to it.

"Mortech is merely one of our many partners that help lenders automate their custom quotes in the Zillow Mortgage Marketplace," he said. "Media reports indicate that Mortech is playing a much more integral part in both LendingTree’s and Google’s operations. For Zillow Mortgage Marketplace, Mortech operates more as a servicer for lenders who want to send quotes faster and more often."

I also asked Rascoff to comment on the possible threat from Google entering the mortgage quote business. He said they have not seen Google's offering yet, but from media reports it appears to be very different from the Zillow Mortgage Marketplace.

"It has been an incredibly complex and time-consuming mission to get Zillow Mortgage Marketplace to the level of success it enjoys today," he said. "Our model requires a lot of continuous monitoring and hard work to keep the ecosystem functioning as well as it does."

So far, the marketplace has attracted nearly 500,000 loan quotes from consumers. There are about 5,300 active lenders who participate, with those lenders returning some 6.3 million quotes to potential borrowers.