Santander Consumer received a civil subpoena from the Department of Justice about its subprime auto lending business, part of a probe into practices in the booming area of financing car purchases for people with spotty credit.

Federal prosecutors are seeking documents related to debt underwritten and securitized since 2007, according to a regulatory filing. General Motors Co. (GM)'s financing unit said it received a similar communication earlier this week.

Laurie Kight, a spokeswoman for Santander Consumer, and Betsy Feuerstein, a spokeswoman for the U.S. Attorney in Manhattan, declined to comment on the Santander Consumer subpoena.

The U.S. government is looking into companies that specialize in subprime auto lending using a 1989 law known as FIRREA that it relied on to go after mortgage lenders. The law imposes a lower burden of proof than a criminal prosecution and threatens penalties of more than $1 million for each fraudulent statement or act.

The growth in auto lending to subprime borrowers is being fueled by a surge in demand for securities linked to debt. Issuance of asset-backed bonds tied to such loans had reached $10 billion this year through May 30, up 5 percent from the pace a year earlier, according to Wells Fargo & Co. Total sales of $17.6 billion last year are more than double the $8 billion sold in 2010, when securitized-debt markets started to revive after all but shutting down in the 2008 financial crisis.

Santander Consumer, based in Dallas, and GM Financial are the top issuers of the bonds, according to data compiled by Bloomberg.

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