Federal prosecutors have begun a civil investigation into the booming business of subprime auto lending, focusing on the packaging and selling of questionable loans to investors.

The inquiry is being undertaken amid worries among some regulators that checks and standards are being neglected as the subprime auto loan market surges, in a small, yet disturbing, echo of the subprime mortgage crisis.

General Motors’ finance subsidiary disclosed in a securities filing Monday it had received a Justice Department subpoena for documents on the origination and the securitization of subprime loan contracts since 2007. The subpoena asks for the underwriting criteria and how the loans were represented to those who were pooling them and assembling securities to be sold to investors.

The office of Preet Bharara, the U.S. attorney for the Southern District of New York, also is looking at other companies, say people briefed on the matter. In the GM investigation, Bharara is reviewing whether the lender sold questionable auto-loan investments to investors, they said; at the center of the investigation is whether the lender fully disclosed to investors the creditworthiness of the borrowers whose loans made up the complex securities.

It is unclear who else has been asked for information, but General Motors Financial also indicated that the inquiry was looking broadly at the subprime auto finance industry.

“Our understanding is that the request is focused on the subprime finance space in general,” Susan Sheffield, an executive vice president at GM Financial, said in an email on Monday.