KNOXVILLE (AP) — FBI and Internal Revenue Service agents on Monday locked down the headquarters of Pilot Flying J, the truck stop business owned by the family of Tennessee Gov. Bill Haslam and his brother, Cleveland Browns owner Jimmy Haslam.

FBI spokesman Marshall Stone told The Associated Press that the move was part of an ongoing investigation, but he would not provide additional details. FBI and IRS agents were expected to remain in the building into the evening, he said.

The FBI was keeping all traffic away from the company property, and Knoxville police patrol cars and officers could be seen outside the headquarters.

"Any details that would be released to the public would not be available for some time," Stone said.

The company doesn't know why FBI officials closed the headquarters but is cooperating with authorities, spokeswoman Lauren Christ said in a statement. Pilot Flying J retail operations remain open, she said.

Jimmy Haslam stepped down as company CEO after buying the Browns from previous owner Randy Lerner in a $1 billion deal in August. He was previously a minority owner of the rival Pittsburgh Steelers but sold that.

Pilot then brought in John Compton, who had been with PepsiCo Inc. for 30 years and its president for less than a year, to replace Haslam as CEO.

In February, Pilot announced Jimmy Haslam was returning as Pilot CEO and Compton would become a consultant.

NFL spokesman Greg Aiello said the league was aware of the investigation but had no other information or comment.

Bill Haslam has no position with the company but still has an unspecified holding in it, according to his limited financial disclosures.

David Smith, a spokesman for the governor, said he was "aware of the situation in Knoxville today" but declined to comment further. He referred any questions for more information to Pilot.

During the 2010 governor's race, Bill Haslam refused to divulge how much money he earned from Pilot, the family-founded chain with annual revenues of $20 billion.

He argued that releasing his Pilot earnings would reveal personal information about the income of family members not running for office, and proprietary information about the privately held company.

Since being elected governor, Haslam has also kept his Pilot holdings outside of a blind trust he has created for other investments.

Pilot was founded in 1958 by the Haslam brothers' father, Jim Haslam. The company bought Flying J for $1.8 billion, closing the deal in 2010, and says it now has more than 600 interstate travel centers and 25,000 employees.

In 2009, Pilot settled a price gouging lawsuit brought by the Tennessee attorney general and paid fines in Georgia and Kentucky.

Haslam said during the 2010 campaign that the pricing problems were quickly addressed and new software was created to avoid a repeat of what occurred in the aftermath of Hurricane Ike in 2008.

"I promise you that for a company that's based on 52 years of community service and low prices we would never do anything intentionally to put that risk," Haslam said in a October 2010 debate.