BP has been fined $US87 million for failing to correct safety hazards at a refinery in Texas.
An explosion in 2005 at the plant killed 15 people and injured 180 more.
The Occupational Safety and Health Administration cited 270 violations at the oil refinery.
BP said it believed it was in "full compliance" with a 2005 settlement agreement with OSHA and would work with the agency to resolve the issue.
The BBC reports the $US87 million fine is the largest in OSHA's history.
In 2005, BP paid a fine of $US21.3 million to OSHA and entered a four-year agreement to repair hazards at the Texas City refinery, which is the third largest in the US.
The latest fine follows a six-month inspection into whether BP complied with that agreement.
BP now has 15 days to either agree to pay the fine and take corrective action, or to contest the penalty through a hearing process.
The company was fined $US50 million by the Department of Justice in 2007 to settle criminal charges stemming from the explosion.
The company has also paid more than $US2 billion to settle civil lawsuits and says it has invested more than $US1 billion to repair safety problems at Texas City.
Earlier this week, BP reported third-quarter profits of $US4.98 billion. However, its shares fell 1% to 579.7 pence after the announcement.