While most attention in the ongoing student debt crisis narrative has focused on new graduates, it turns out the federal government has been quietly targeting a different group of debtors: retirees.

The Treasury Department has been withholding as much as 15 percent of Social Security benefits from "a rapidly growing number of Social Security recipients who have fallen behind on federal student loans," Smart Money's Annamaria Andriotis reports:

"From January through August 6, the government reduced the size of roughly 115,000 retirees' Social Security checks on those grounds. That's nearly double the pace of the department's enforcement in 2011; it's up from around 60,000 cases in all of 2007 and just 6 cases in 2000...

The amount that the government withholds varies widely, though it runs up to 15%. Assuming the average monthly Social Security benefit for a retired worker of $1,234, that could mean a monthly haircut of almost $190."

Since 2001, the number of retirees who've seen benefits garnished has ballooned from about 20,000 to nearly 100,000. The worst part? Some of these retirees are simply among the growing number of older consumers who've taken on loans to help their kids or grandchildren through college.

A recent report by the New York Federal Reserve found more than 17 percent of student loan borrowers are over the age of 50.

And while slates for credit and other forms of debt can be wiped clean in bankruptcy, lawmakers have yet to add student loan debt to the list.

Still, simply owning study loans in old age doesn't automatically put retiree's benefits on the fed's chopping block.

"It's when people aren't making any attempt whatsoever [to pay] that they start heading down that road," said Justin Hamilton, spokesman for the Dept. of Education.