Chicago's Board of Ethics is handing a former Uber executive a $90,000 fine for illegally lobbying the city's mayor over ride-sharing privileges at the city's two airports.

On Thursday, the ethics panel voted 5-0 to levy the fine on David Plouffe, who was Barack Obama's former campaign manager. The fine came because Plouffe was not registered with the city as a lobbyist when he e-mailed Mayor Rahm Emanuel's personal account. Plouffe received an immediate reply to his e-mail from Emanuel, even though the mayor was overseas at the time.

Lobbyists must disclose their activities. But the lobbying by Plouffe came to light in December as part of open-records lawsuits. In response to those suits, the mayor released hundreds of personal e-mails connected to his public position.

"Registration of lobbyists is important. It's a disciplined process that requires someone to identify themselves as a lobbyist, name the clients they're working for and those organizations they anticipate lobbying. It gives these people access to the decision-makers who can affect legislative or administrative processes that other people don't have," said William Conlon, chairman of the city's ethics board.

The November 2015 e-mail exchange concerned Emanuel's prior decision to authorize Uber and Lyft to work O'Hare and Midway Airports, which were once under the exclusive control of the taxi industry. Among other things, the then-vice president of policy and strategy for Uber was concerned about a city demand that Uber drivers at airports have placards noting they are Uber vehicles. (Uber, whose mobile app has raised privacy concerns, eventually instructed its Chicago airport drivers to have "the Uber emblem on the passenger side of your front windshield.")

"Assume both of us thought the airport issue was settled and we would never have to discuss again, but unfortunately two significant new hurdles were introduced," Plouffe wrote to the mayor.

(The pair had worked in then-President Barack Obama's White House when Emanuel was Obama's chief of staff. What's more, Emanuel's brother, Ari, is a well-known Hollywood investor in Uber.)

"Coming to you because of their severity that would prevent us from operating. We were all set to announce Monday we were beginning pickups," Plouffe added. "Sure this comes as much of a surprise to you as us, since there was an agreement in place."

Emanuel promptly replied, "Impossible for me to address from China." He wrote Plouffe to speak with his top aides.

In response to the fine, Uber said it works "hard to ensure our registrations are accurate and up to date. We regret that in this instance we made a mistake, and we will comply with the board's assessment."

Uber contested the amount of the fine, however, arguing it should have been $1,000. Emanuel said in a statement that "the Ethics Board did exactly what it was supposed to do."