(AP) -- The former chairman of the agency that controls New York City-area airports conspired with a United Airlines lobbyist to get the airline to run direct flights to South Carolina so that the executive could more easily visit his vacation home, prosecutors said Thursday.

David Samson -- a political mentor to New Jersey Gov. Chris Christie -- pleaded guilty to a corruption charge that he wrongfully used his Port Authority of New York and New Jersey post.

The ex-lobbyist, Jamie Fox, was charged with conspiracy to commit bribery. The Democrat went on to become Christie's transportation commissioner after ending his lobbying work for United.

Samson and Fox "both should have known better. They both did know better," U.S. Attorney Paul Fishman said. "It was an unacceptable abuse of public authority."

Fishman also announced that United would pay a $2.25 million fine for the role its officials played in the scheme.

United's then-CEO, Jeff Smisek, and two other executives left the airline last year after United conducted its own investigation. None of them has been charged with any criminal wrongdoing.

The company said in a statement that it accepted responsibility for certain conduct that led to the flight and agreed to "continue to enhance its compliance, anti-bribery and anti-corruption program policies and procedures."

Samson admitted that he conspired with Fox to pressure United to reinstate the "chairman's flight" to Columbia, not far from Samson's vacation home in Aiken, by removing from a board agenda discussion of a hangar that United wanted at Newark Liberty International Airport, Fishman said.

Prosecutors will recommend that Samson get a sentence of probation to 24 months behind bars under a plea agreement. Sentencing is scheduled for Oct. 20. His attorney, Michael Chertoff, said he wouldn't have any comment until then. Samson left the courthouse after posting $100,000 bond and surrendering his passport.

Fox's attorney Michael Critchley said his client would never jeopardize his reputation by engaging in illegal behavior and was part of an arrangement that he thought was appropriate.

A spokesman for Christie didn't immediately respond to a request seeking comment.

United ended the half-filled Columbia flights three days after Samson resigned his Port Authority post in March 2014 in the wake of the George Washington Bridge lane closure scandal that led to criminal charges against three other Christie allies.

Samson wasn't charged in the bridge investigation, in which the Christie allies were accused of causing traffic problems to exact revenge against a politician. But an email from a Port Authority official to a Christie aide, both of whom were later charged, described Samson "helping to retaliate" after Port Authority executive director Patrick Foye ordered the lanes reopened.

Samson, a former state attorney general, led the governor's transition team in 2009, and Christie appointed him to the Port Authority chairman's post in 2011.

He resigned from the Port Authority a day after a law firm's taxpayer-funded report cleared Christie of wrongdoing and laid much of the blame for the lane closures on the Christie aide. Samson wasn't interviewed for the report.

The bridge investigation, combined with an earlier audit that called the Port Authority "challenged and dysfunctional," trained a spotlight on the powerful agency and eventually led to questions about Samson's interactions with United Airlines.

When Samson was chairman, United resumed direct flights to the South Carolina airport. Around the same time, Chicago-based United was pressing for concessions from the agency, including the new hangar at Newark, rent reductions and a commuter rail-line extension that would connect the airport directly to lower Manhattan.

The Port Authority also wanted to increase flights to Atlantic City, while New Jersey struggled to revitalize the seaside gambling resort. United began those flights between Houston and Chicago in April 2014, but they were typically half full and United canceled the service that December.

"It undermines the already eroded confidence the public has that government is being operated for their benefit," said New Jersey Assemblyman John Wisniewski, a Democrat who helped lead an investigative committee that investigated the bridge case. "The governor is either a bad judge of character when it comes to making high level appointments or is not as forthcoming as he'd like us to believe."

___

Associated Press writer Maryclaire Dale, in Philadelphia, contributed to this story.