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United Airlines chairman and CEO Jeff Smisek is stepping down amid probe

The company did not specify why Jeff Smisek was leaving.

The chairman and CEO of United Airlines is stepping down in connection with an investigation into the airline's dealings with the agency that operates New York airports.

United Continental Holdings Inc. said Tuesday that Jeff Smisek and its executive vice president of communications and government affairs and its senior vice president of corporate and government affairs had resigned. It said former railroad executive Oscar Munoz was named CEO and president.

The company did not specify why Smisek was leaving. But, after announcing the departures of the other two executives in the statement, the company said, "The departures announced today are in connection with the company's previously disclosed internal investigation related to the federal investigation associated with the Port Authority of New York and New Jersey."

United disclosed earlier this year that the company and some of its executives had received subpoenas from a federal grand jury for information about dealings with the Port Authority, which oversees major airports in the two staes. At the time, United said it was conducting its own internal investigation.

Former Port Authority Chairman David Samson's activities have been subject of document requests from the U.S. attorney's office in New Jersey, including Samson's votes on United Airlines projects at Newark Airport.

The votes occurred at the same time United was restarting flights from Newark to Columbia, South Carolina, near where Samson has a vacation home. United began a roughly twice-weekly direct flight from Newark to Columbia after Samson became chairman. It was canceled days after he resigned last year.

This article originally appeared on NBC News.com.