Families for Excellent Schools, a charter-schools organization known for its battles with Mayor Bill de Blasio and its close relationship with Eva S. Moskowitz, the mayor’s frequent antagonist and head of the city’s largest charter school network, Success Academy, said on Monday that it was shutting down.

The organization announced last week that it was firing Jeremiah Kittredge, its chief executive officer, after an accusation of “inappropriate behavior toward a non-employee.” But the decision to close seemed to reflect financial problems rather than the loss of a single employee.

Families for Excellent Schools for years was the well-funded face of the charter school movement in New York, but its support seems to have evaporated. The organization’s chairman, Bryan Lawrence, said in a statement: “Unfortunately, after a series of challenges over the past year and particularly given recent events, we have determined that the support necessary to keep the organization going is not there.”

In 2014, the year that Mr. de Blasio took office, Families for Excellent Schools spent $9.6 million on lobbying, more than any other organization in the state. Much of that money was spent on television advertisements criticizing the mayor for blocking several of Ms. Moskowitz’s schools from getting space in city-owned school buildings. (As a candidate, Mr. de Blasio had promised to halt a practice of giving charters space in public school buildings.)