US authorities have demanded Glencore hand over documents about its business in the Democratic Republic of Congo, Venezuela and Nigeria as part of a corruption probe.
The news sent the mining company's shares down more than 8%.
Swiss-based Glencore said it received a subpoena from the US Department of Justice, requesting documents and records on compliance with the US Foreign Corrupt Practices Act and money-laundering statutes.
A Justice Department spokeswoman declined to comment on the existence of an ongoing investigation.
Glencore said the documents requested from its US division related to the commodity trader's business in the three countries from 2007 to present.
Glencore, which listed in London in 2011, said it was reviewing the subpoena.
The US Foreign Corrupt Practices Act makes it a crime for companies to bribe overseas officials to win business.
Shares in Glencore, the world's largest producer of cobalt with large operations in the DRC, at one point on Tuesday were down more than 13%, their largest one-day fall in more than two years. The stock eventually closed 8% lower at 321 pence.
Analysts at Barclays and Credit Suisse viewed the initial share price drop as steeper than warranted.
The DRC accounts for about 25% of Glencore's net present value, analysts say, while Venezuela and Nigeria's contribution to the bottom line was negligible.
Some analysts believe the investigation could be a result of Glencore settling a mining row in the DRC with Israeli billionaire Dan Gertler, under US sanctions since last year, by agreeing to pay royalties in euros.
Investors are also monitoring developments in Britain where the Serious Fraud Office was reported to be preparing to open a formal investigation into Glencore's activities in the DRC.
On the Nigerian side, the US has also been looking into the country's former oil minister Diezani Alison-Madueke, who was briefly arrested in London in October 2015, and her associates.
She has denied any wrongdoing and is yet to be charged by British authorities.
The Justice Department issued a claim last year for assets that it alleged to be the proceeds of corruption belonging to Alison-Madueke and two of her associates.
In its claim, the department said Glencore bought more than 7 million barrels of crude from one of the companies used as a vehicle for alleged corruption. It was not immediately clear whether the subpoena concerned that case.
Glencore declined to comment on the Nigerian crude liftings.
Glencore's founder, Marc Rich, was indicted in 1983 for exploiting the US embargo against Iran, tax evasion, fraud and racketeering.
He fled to Switzerland, where he remained a fugitive pursued by the Justice Department until he was pardoned by then-President Bill Clinton in 2001.