United Continental Holdings Inc has said that Jeff Smisek, the company’s chief executive, resigned on Tuesday afternoon, September 8, Chicago time. The company named Oscar Munoz to take over as CEO immediately.

A letter from Munoz to company employees, which was obtained by multiple US media sources, said that Smisek’s resignation, along with those of two executives in government affairs, “are in connection with United’s previously disclosed internal investigation related to the federal investigation associated with the Port Authority of New York and New Jersey.”

United allegedly created a flight between its hub in Newark, New Jersey, and the South Carolina home of former Port Authority chairman David Samson, in hopes of the Port Authority providing millions of dollars in funding for several projects that were beneficial to United, according to a Bloomberg report that cited multiple sources. The flight was cancelled shortly after Samson’s 2014 retirement from the Port Authority.

Media reports in the US say that prosecutors have declined to confirm or deny that a Port Authority probe exists. 

Smisek will receive a lump sum severance payment of US$4.875 million in cash, as well as other benefits. 

Munoz joined United Continental from rail company CSX, but has served on the United Continental board since 2010, and on Continental Airlines’ board from 2004 until that company’s 2010 merger with United.