Listen folks up, especially anyone in the financial sector in town. If the feds force Bank of America, Wells Fargo, and other zombie banks to eat their own dog food — $21 billion worth of it — get ready for more belt-tightening.

All last year it was obvious that the zombie banks were sticking Fannie and Freddie with questionable mortgages, admittedly in service of the drive to “fix” other bad mortgages and prop up the real estate market. But now the feds have put a number on those iffy loans, and it is five times the $4b. buyback the banks undertook in 2009, Bloomberg reports. More:

“We are trying to be good stewards of taxpayer dollars and as part of that, it’s important that those dollars not go to loans that should not have been sold to us in the first place,” said Sharon McHale, a spokeswoman for McLean, Virginia-based Freddie Mac. … Bank of America recorded a $1.9 billion “warranties expense” for past and future buybacks of loans that weren’t properly written, seven times the 2008 amount, the bank said in a Feb. 26 filing. A spokesman for Charlotte, North Carolina- based Bank of America, Scott Silvestri, declined to comment.

Darn tooting. WFC wasn’t much better off last year, with $1.3b. in expenses. Here’s what happens next: the banks run to Congress and try to get taxpayers to eat their bad loans via government-owned Fannie and Freddie.

Woof-woof.