A group of 28 senators are appealing to FAA Administrator Michael Huerta to drop the agency’s plan to charge the Experimental Aircraft Association (EAA) for federal air traffic controller expenses during next month’s AirVenture in Oshkosh, Wis.

In a June 6 letter, the senators say the plan marks a “shift in policy by the FAA to charge for air traffic services [that] is tantamount to an imposition of a new user fee on general aviation.”

FAA last month informed EAA that it would charge $500,000 for travel costs, per diem expenses and overtime pay for the federal controllers brought in during this year’s weeklong event. The ATC tower in Oshkosh is run through the contract tower program, but FAA brings in additional staff — including nearly 80 controllers and supervisors — to handle the 8,000-10,000 aircraft that fly into AirVenture.

The agency similarly charged for these expenses in April during the Sun N’ Fun Fly-in in Lakeland, Fla., while the tower there was under threat of closure.

EAA questioned FAA’s ability to “unilaterally impose assessments, fees, and other costs on general aviation” and appealed to Congress for help. “AirVenture and other aviation events are being held hostage in large part because of the FAA’s decisions, as the agency would not supply the necessary personnel or approvals to events unless they signed the FAA’s contract and paid the bill in advance,” says EAA Chairman Jack Pelton. “Members of Congress from both parties saw this for what it is — a user fee on general aviation — and have stepped forward in opposition.”

EAA had established a “Rally Congress” website asking aviation enthusiasts to write, email or electronically sign a petition urging their senators to oppose the FAA’s plan. More than 19,000 signed the petition or wrote their lawmakers in response to the EAA appeal.