Back in September United threatened to pull out of Newark over $20 million in fuel taxes targeted at its operations. They were never going to leave, but made their (perfectly reasonable) point about New Jersey trying to extract revenue from just them.
United has also complained that Newark airport is overcharging them, and the FAA agrees. This past fall the FAA found that the Port Authority of New York New Jersey which manages the airport “routinely diverted airport revenue to non-airport activities.” There’s a law that lets them do this, but the airport appears to be going well beyond it.