General Motors (GM), the world's biggest carmaker, is having its accounts investigated by regulators.
Regulators are checking the nuts and bolts of GM's accounts
The Securities and Exchange Commission (SEC) has issued a subpoena, and the firm said it was co-operating fully.
Regulators are looking into areas including how GM accounts for pension liabilities and transactions between itself and bankrupt supplier Delphi.
GM said subpoenas were also served on firms related to its finance division, General Motors Acceptance Corp (GMAC).
The SEC already is investigating other firms, including another carmaker, and is trying to improve its understanding of how companies book pension liabilities.
Analysts said the concern is that firms may inflate or cut their liabilities in order to boot profits or cut losses.
On top of that is the Chapter 11 bankruptcy filing by Delphi, which has muddied the waters regarding the amount of money GM needs to stump up to cover retirement costs.
Delphi was spun off from GM in 1999, and the carmaker underwrote pension costs for many of the firms' workers.
Since Delphi has asked for protection from its creditors, GM has said that it may be liable for as much as $12bn (£6.7bn) in pension costs for the auto parts firm's workers.
GM already is creaking under its own pension requirements and has lost almost $4bn in the first nine months of this year.