For Gov. Andrew M. Cuomo, who has made building major projects a centerpiece of his tenure, it is a signature plan — turning La Guardia Airport into a world-class, 21st-century travel hub.

A crucial part of that is a $2 billion AirTrain, an elevated people-mover that would connect La Guardia to New York City’s subway system and commuter rail.

That plan has been moving forward rapidly. But now, an influential Democrat, Representative Alexandria Ocasio-Cortez, is questioning why the governor’s plan was the only option among dozens for getting travelers to and from La Guardia to have survived a federal review.

Ms. Ocasio-Cortez, a vocal freshman in Congress who represents parts of Queens and the Bronx, is demanding in a letter to federal officials answers to why 46 alternatives to Mr. Cuomo’s AirTrain project were ruled out so quickly over the opposition of many Queens residents and community groups.