Any homeowner considering a “strategic default” is wise to think twice. Well, make that three times, as Fannie Mae (Stock Quote: FNM) is cracking down harder on borrowers who walk away from their obligations.

Fannie, the government-backed company that bundles home loans and sells them to investors, announced it will take tougher action against borrowers who walk away from mortgages they can afford. These strategic defaulters will be barred from obtaining new mortgages for seven years, up from four.

Because Fannie dominates the mortgage-buying market, a would-be borrower could find it difficult or impossible to obtain a mortgage after ending up on Fannie’s black list.

“We’re taking these steps to highlight the importance of working with your servicer,” Terence Edwards, Fannie’s executive vice president for credit portfolio management, said in announcing the tougher policy. “Walking away from a mortgage is bad for borrowers and bad for communities, and our approach is meant to deter the disturbing trend toward strategic defaulting.”

No one knows just how many strategic defaults there are, but some experts think they account for about 12% of all defaults. Strategic defaults are most common among homeowners who owe more than their homes are worth, since they may feel it is pointless to keep up payments even if they can afford them. Nationwide, nearly 25% of homeowners with mortgages owe more than their properties are worth, providing a large pool of potential defaulters, and some experts say strategic defaults are becoming more socially acceptable.

Prior to 2008, a borrower who went through foreclosure on a loan backed by Fannie Mae had to wait five years before becoming eligible for a new one. In 2008, Fannie reduced the wait to four years.

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Under the new rules, a seven-year wait will be required of defaulters who could have paid but simply chose not to. Those who can prove hardship or who tried to work out a compromise with their lender will have to wait only three years. Borrowers who voluntarily surrender their homes through a process called “deed in lieu of foreclosure,” and those who work out short sales, will have to wait only two years. In a short sale, the lender agrees to accept less than it is owed after the borrower sells the property.

Fannie said it also plans to step up legal action against strategic defaulters. In states that allow it, that may include going after assets in addition to the borrower’s home.

Bottom line: walking away from a mortgage can have dire consequences that will last for years. In addition to being unable to obtain a new mortgage, the strategic defaulter may be unable to get a car loan or credit card, and could even find that a poor credit rating will make it harder to get a job.

Before walking away from a mortgage, make every effort you can to negotiate with the lender. And take a look at the government’s Making Home Affordable programs for troubled homeowners.

Unfortunately, these and similar programs are meant for people in financial trouble, like those who have lost jobs or cannot afford payments because of rate resets.

Nobody likes making payments on a home worth less than the loan. But simply walking away could make your situation even worse.

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