A group of charter school leaders is trying to pour cold water on the idea that Mayor Bill de Blasio has warmed to charter schools.

Days after de Blasio gave an education speech that drew praise from some charter school leaders, others sharply criticized the mayor Tuesday charging that he has not done enough to support their growth. At the heart of their criticism is an ongoing battle for limited space inside of city-owned school buildings, which the de Blasio administration has been reluctant to offer to charter schools.

In an open letter to de Blasio, the leaders accuse the de Blasio administration of “hurting some of the city’s most vulnerable students” by denying their requests for space in public-school buildings.

The letter was circulated by the advocacy group Families for Excellent Schools, which is organizing a rally scheduled for Sept. 30 — the latest in a series of large-scale events designed to demonstrate the political power of the charter sector. It was signed by Eva Moskowitz, the leader of the Success Academy network of charter schools and a regular critic of  Mayor de Blasio’s, and by five other leaders who have been less apt to criticize the mayor publicly in recent months.

The schools’ requests for space have come in the wake of legislation, passed in 2014, that dramatically altered how charter schools in New York City found space.

Under former Mayor Bloomberg, some charter schools were granted space in public school buildings, and others were forced to use their budgets to pay for private space. The new law, sparked by a fight between Moskowitz and the city early in de Blasio’s term, offers additional perks to charter schools. Now, a new or expanding school can request city space, and if city officials say suitable space is not available, an appeals process allows charter schools to receive city funding to rent space elsewhere.

The administration has offered school space to a small number of charter schools, but de Blasio has leaned more heavily on the appeal process, denying requests from 45 charter schools, according to the New York Post. The result: All but one school will receive city funds to operate in private space, which the city estimates will cost more than $30 million by the end of this school year.

The leaders, who run the Achievement First, KIPP, Public Preparatory, and Uncommon Schools networks, as well as the founder of Coney Island Prep, called the city’s spending on private space “downright shameful” given that space remains available inside many public school buildings. Many charter networks favor space inside public buildings, in part because it saves money on utilities and other miscellaneous costs. Such co-locations, pioneered by the Bloomberg administration, helped the city’s charter sector to grow quickly over the last decade.

It is a striking contrast from the friendly tone that some of those leaders have sought to strike in other ways. Uncommon Schools has provided professional development to district teachers in Brownsville, KIPP founder Dave Levin served on a city-appointed space-sharing working group, and just last month Public Prep CEO Ian Rowe hosted a visit from Chancellor Carmen Fariña to one of his co-located schools on its first day.

But space-sharing arrangements can become tense as schools with different schedules, philosophies, and grade levels divide scarce resources like time in the cafeteria and gym. The Panel for Educational Policy rejected one such co-location request at the end of last school year, citing concerns about the arrangement. De Blasio vowed to listen more closely to concerned school communities while campaigning for mayor.

David Bloomfield, a professor of education leadership at the CUNY Graduate Center and Brooklyn College, said he sees reasons for charter schools to prefer private space, primarily that they don’t have to share common facilities. The mayor is being unfairly criticized, he said, for following procedures outlined in a law that charter school advocates favored.

“This is a law that was written to their specifications, certainly not de Blasio’s,” Bloomfield said. “It seems to be a situation where he can do no right.”

Meanwhile, not all charter school leaders agree that operating in public school buildings is necessary — or even preferable. Steve Zimmerman, the founder of two charter schools in Queens and co-director of the Coalition for Community Charter Schools, a group that represents many unaffiliated charter schools, said that public schools built decades ago often have outdated infrastructure that can be hard to renovate.

Plus, Zimmerman added, there’s only so much space available in public buildings.

“We’re going to be bumping up against reality soon,” he said.

Department spokeswoman Devora Kaye said in a statement that the city was simply complying with state law.

“We have a clear process in place and have been and continue to comply with the State law to provide space or rental assistance for eligible charter schools,” Kaye said in a statement.