The penalty is largest fine the FAA has proposed imposing on Amazon, which the agency said has had a series of hazardous materials violations.

The FAA alleged that on Oct. 15, 2014, Amazon sent a UPS package with a one-gallon container of “Amazing! LIQUID FIRE,” a corrosive drain cleaner for transportation by air from Louisville, Kentucky, to Boulder, Colorado.

The package leaked and nine UPS (UPS) employees who came into contact with the box reported feeling a burning sensation and were treated with a chemical wash, the FAA said.

The FAA said the shipment was improperly packaged, not accompanied by a declaration for dangerous goods and not properly labeled to indicate the hazardous contents.

The FAA alleged Amazon failed to provide emergency response information with the package, and Amazon employees who handled the package had not received required hazardous materials training.

The FAA said that from February 2013 to September 2015, the government found Amazon had violated the hazardous materials regulations 24 other times.

It was not clear how many total times Amazon paid fines or admitted responsibility, since the FAA does not issue press releases for fines below $50,000, an FAA spokesman said. The company did pay $91,000 in April 2014 for a 2013 incident.

The agency is continuing to investigate Amazon’s compliance with hazardous shipment rules. Amazon did not immediately respond to a request for comment.

In April 2014, Amazon paid a $91,000 fine to the FAA after its employees improperly shipped a package in 2013 containing flammable liquid adhesive by air on Federal Express from Whitestown, Ind., to Boulder, Colo.

FedEx (FDX) employees in Boulder discovered a gallon container of the adhesive was leaking and not properly labeled and without proper shipping papers, the FAA said.