The spill has cost the company $6.1bn, including $319m paid out in compensation.
BP also reported a record quarterly loss of $17bn in July and is having to deal with more than 145,000 claims submitted for compensation.
Tony Buzbee, the Houston attorney who filed the class-action suit over the April-June spill, welcomed the labour department's action.
"We believe the fine to be appropriate and welcome the government's efforts in our quest to force this British company to comply with US and Texas Law," he said.
"BP's record rivals the worst in US history."
BP's global head of refining said the company would work with OSHA to improve refinery safety, but Osha will continue to seek $30m in fines for new safety violations found by government inspectors at the company's refinery.
Ian Conn, global head of refining, said: "BP has a stated goal to become a leader in process safety and we look forward to working collaboratively with Osha to achieve an injury-free workplace in our operations."
BP has defended its efforts to improve safety at the 465,000 barrel per day (bpd) refinery, located about 50 miles south of downtown Houston.
Last week, Greg Abbott, the Texas attorney general, sued BP for a 40-day release of excess pollution including carcinogenic benzene in April and May at the Texas refinery.