The state agency that oversees airports is casting doubt on the official makeup of the Martha’s Vineyard Airport Commission, following a vote by the Dukes County Commission early this month to replace incumbents with new members.

In a strongly worded letter sent this week, Christopher Willenborg, administrator for the Aeronautics Division of the Massachusetts Department of Transportation, challenged the county commission to defend the appointments of Robert Rosenbaum, Clarence A. (Trip) Barnes 3rd and Myron Garfinkle to the airport commission.

“Please immediately provide me, in writing, with your rationale for appointing Myron Garfinkle, Robert Rosenbaum and Clarence Barnes,” Mr. Willenborg wrote in part.

The county commission appoints the seven members of the airport commission, who serve staggered terms.

In the appointment process that took place, two incumbents, Constance Teixeira and James Coyne, were ousted. Former airport commissioner Denys Wortman, whose term also expired this year, chose not to run again.

“Given the litigious history between the county and the airport commission, it is incumbent upon the Aeronautics Division to ensure that this activity is not a reorganization of the airport commission, nor is it an attempt to interfere with the autonomy and authority of the airport commission,” Mr. Willenborg also wrote in the letter, sent by email on Wednesday.

As a result of the letter, airport manager Sean Flynn canceled a meeting of the airport commission scheduled for Friday morning.

“We have to make sure that the law is adhered to and that the decisions made here are valid,” Mr. Flynn said, speaking to the Gazette by phone Thursday.

The letter appears to turn up the heat on a legal dispute that has been simmering between the airport and the county for months. The two agencies have been in court since last May, when the airport commission filed a lawsuit against the county to gain further legal recognition of its independence. The airport sought to determine how much oversight the county can exert over the airport commission.

Last fall, county commissioners tested the limits of that authority when they decided to expand the size of the airport commission from seven to nine members.

A superior court judge blocked the move, ruling that the appointments constituted a reorganization of the airport commission, possibly violating a set of grant assurances which enabled the airport to receive federal and state grants for the construction of a new terminal nearly two decades ago. Under the grant assurances, signed by the county and the airport, reorganization of the airport commission is not allowed without prior approval from state aeronautics officials.

Now Mr. Willenborg, the aeronautics administrator, is questioning whether the recent routine reappointments also constitute a reorganization.

In a telephone interview, Mr. Willenborg, who was joined by two press spokesmen and aeronautics lawyer Tracy W. Klay, pointed to the fact that during interviews with the county commission, the incumbent candidates were questioned about their stance on the ongoing lawsuit.

“Given the litigious history at the airport and the questioning that is in place recently, it appears that this is an attempt for reorganization and we have asked the county to clarify,” he said.

In his letter asking the county to provide a rationale for the three appointments, Mr. Willenborg also referenced the outgoing commissioners’ aviation experience, noting that Mr. Coyne is an “exceptionally well-qualified aviation professional,” and that Ms. Teixeira is “the former chair with a substantial aviation background.”

But by telephone yesterday he downplayed the aviation qualification issue, saying the central issue is “in regards to the lawsuit and the grant assurances.”

To that end, he is asking the county to justify their appointments.

For now, Mr. Willenborg’s letter has placed the airport commission on standby. “Please be advised that, in my opinion, any vote taken by the commission reorganized without the approval of the Aeronautics Division would be invalid,” he wrote.

Mr. Flynn said the state has the ability to resolve the issue, but he wasn’t sure how. He said the airport would be receiving guidance from their attorneys about how to proceed.

“From what I understand, it’s a fairly clear, clean process, and hopefully timely,” he said.

Mr. Flynn said he didn’t know how state aviation officials had learned of the developments.

“I know both the FAA and the Aeronautics Division monitor all newspapers in Massachusetts,” he said.

But Mr. Willenborg said he had learned about the new appointments in a phone call from Mr. Flynn, and from reading the local press.

He declined to elaborate on the process going forward.

“We are not going to speculate on the next steps,” he said. “We want to see the response back from the county.”

Meanwhile, Mr. Flynn said the airport can operate normally without the airport commission.

“The commission is a policy board,” he said. “It has nothing to do with the day-to-day operations of the airport.”

If there is an urgent matter that needs the commission’s attention, the airport manager said he would figure out if he could assemble a four-member quorum for a meeting. There are four airport commissioners whose membership is not in question. They are Beth Toomey, Christine Todd, Richard Michelson and Norman Perry.

“I have to look at the members individually and see if there is a challenge to their appointment,” Mr. Flynn said. “You have three members that they are questioning, so that still leaves four members out there.”

The county commission has not yet responded to the letter and plans to discuss it at their meeting next Wednesday, county manager Martina Thornton said Thursday.