Northwest Airlines, now a part of Delta Air Lines , has agreed to plead guilty to conspiring to fix the prices of air cargo, the U.S. Justice Department said on Friday.

Northwest agreed to plead guilty to a single felony count that its now-shuttered Northwest Airlines Cargo conspired to fix prices, the department said. It agreed to pay a fine of $38 million.

As a part of the conspiracy, Northwest Airlines Cargo monitored and enforced adherence to the agreed-upon rates, the department said in a statement.

Delta said the price-fixing occurred before it bought Northwest in 2008. Northwest terminated the employment of the individual who it believed had primary responsibility for the conduct in question, Delta said in an email.

Sixteen airlines have pleaded guilty or agreed to do so in the department's long-running probe into price-fixing in air cargo, the Justice Department said.

The airlines have paid more than $1.6 billion in criminal fines, and four executives have been sentenced to prison.

Antitrust enforcers in Australia and the European Union, among others, have also prosecuted air cargo price fixing cases.

Major airlines caught up in the probe include British Airways , Korean Air Lines <003490.KS>, Qantas Airways Ltd , Japan Airlines , Cathay Pacific Airways <0293.HK>, Air France and EL AL Israel Airlines Ltd . and Nippon Cargo Airlines Co. Ltd.

(Reporting by Diane Bartz; Editing by Tim Dobbyn)