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.