When Bill de Blasio was campaigning for mayor, he supported a one-year “moratorium” on locating multiple schools in the same building. He also said it was time for charter school network leader Eva Moskowitz to “stop having the run of the place,” because so many of her Success Academy schools were given space in city schools.

Once elected, however, de Blasio learned that Moskowitz is a very formidable opponent. When he blocked her from opening three new schools in city buildings this year, Moskowitz rallied her troops - including Gov. Andrew Cuomo. And the state legislature passed a law requiring the city to give charter schools space in public school buildings, or pay their rent to go elsewhere.

Now, Moskowitz is knocking loudly on the door of City Hall. She’s waiting to learn the status of 14 charters that were approved in October, plus two growing schools. Will they get space in public school buildings? The state-mandated deadline for the city to respond is the end of December.

She released on Wednesday a letter from the parents at two of her Brooklyn elementary schools that want middle schools.

“Our children are on the road to success,” they wrote. “But to continue that success, our children need middle schools that will pick up where their elementary schools leave off.”

Despite the looming deadline and PR offensive, the Department of Education did not seem in any rush to give Moskowitz an answer.

“We are committed to lifting up all our children, across every neighborhood, who will be the future of this city together,” spokeswoman Devora Kaye said. “Chancellor Fariña is committed to doing what is best for children and we’ll continue to follow the process in place.”

This is the department’s go-to answer for anything involving charters. Behind the scenes though the mayor faces a tough political knot. As far as siting charters, the mayor said in September that he would favor those that share his values, for example by enrolling a larger share of children with special needs and English Language Learners.

At the same time, his administration appointed a task force to look at space-sharing issues. Its recommendations didn’t mention charters but highlighted how school space is at a premium. More recently, the mayor unveiled a plan to expand community schools which will require more space for clinics and other support services.

It's important to note Moskowitz isn't the only charter operator applying for space. The city has repeatedly declined to tell WNYC how many charters are seeking space in public school buildings but at least two others were rejected this fall.

So, how will de Blasio abide by the state law to fit dozens of additional charter schools into public school buildings, after he has promised to scale back co-locations and expand community schools?

Some active parents told WNYC they think the city should pay for the charters to rent private space even though that could cost $40 million in rent. De Blasio has to decide if that’s worth the price. If not, it will cost him with parents who support charters, many of whom are his key constituents.