Law enforcement officers from multiple federal agencies executed search warrants on Caterpillar's HQ in Peoria, Ill., and two other Caterpillar offices Thursday as part of an ongoing investigation into Caterpillar's tax strategy, according to the Peoria Journal-Star.

The investigation stemmed from a 2009 wrongful termination lawsuit filed by former Caterpillar employee Daniel Schlicksup. In that suit, Schlicksup alleged the company shifted profits overseas to avoid paying over $2B in federal taxes. The officers executing the warrants asked Caterpillar employees to leave the buildings.

In 2014, three Caterpillar officials testified before a Senate subcommittee regarding the company's strategy of shifting billions of dollars in profits from the U.S. to Switzerland, where it negotiated a more favorable corporate tax rate of 4% to 6%.

News of the raids sent Caterpillar stock falling nearly 4% to $94.60/share. Caterpillar announced in January it would leave Peoria and relocate to the Chicago area, although a final site has not been selected.

In addition to Caterpillar's HQ, officers executed warrants at a Caterpillar data center in East Peoria and a logistics center in Morton, Ill. The officers participating in the raid include the IRS' Criminal Investigation Division, the Office of Export Enforcement at the U.S. Department of Commerce's Bureau of Industry and Security, and the Federal Deposit Insurance Corp.'s Office of Inspector General.