Caterpillar shares fell Thursday after the company confirmed that law enforcement conducted a search of its facilities, including its headquarters in Peoria, Illinois.
The stock shed more than 4 percent in afternoon trade and was the biggest decliner in the Dow Jones industrial average Thursday.
The company told CNBC that law enforcement was executing a search warrant. Caterpillar said it is cooperating with the search.
Later Thursday, the company said in a statement that authorities were collecting documents and electronic information.
The U.S. Attorney's Office for the Central District of Illinois confirmed the activity to CNBC, saying law enforcement went to facilities in Peoria, East Peoria and Morton.
Caterpillar said the warrant may have been related to and Internal Revenue Service investigation on profits earned by a Swiss subsidiary.
Agents could be seen wearing IRS jackets in video obtained by NBC affiliate WEEK.
Last month, the company said in its annual filing with the Securities and Exchange Commission that the IRS notified Caterpillar of proposed adjustments for its income tax returns between 2010 and 2012. The company said that as part of these audits, the IRS suggested that the company pay taxes on profits earned by it Swiss-based subsidiary.
Caterpillar said in its February annual filing that it is "vigorously contesting the proposed increases to tax and penalties for these years of approximately $2 billion." The company said in the filing that it believes "the relevant transactions complied with applicable tax laws and did not violate judicial doctrines."
Based on the information available at the time, Caterpillar said it believes the result will not have a "material adverse effect on [its] consolidated financial position, liquidity or results of operations."
— CNBC's Jim Forkin contributed to this report.