New York Mayor Bill de Blasio urged educators to consider holding classes outdoors as a way to alleviate concerns around bringing students back to school buildings next month as the colossal school system scrambles to get ready for a Sept. 10 start.

The city announced Monday that it was setting up a program to make it easier for the city’s principals to apply for permits to close streets and reserve park space should they want to move their students outdoors.

“Kids have always loved learning outdoors and being outdoors,” de Blasio (D) said in a news briefing Tuesday. “It’s also great in terms of health and safety.”

De Blasio announced earlier this month that he would reopen the school system, which serves more than 1 million students, for face-to-face instruction, having students attend part time and in shifts to allow for social distancing. New York’s is one of the only urban school systems to announce an in-person start to the school year, and its efforts to reopen schools are being closely watched.

The city is still offering a full-time virtual option for families who want to keep their children home. The mayor cited the city’s plunging coronavirus infection rates, saying it was finally safe to return children to schools. A large portion of the city’s schoolchildren rely on schools for meals and refuge.

But he is facing a major backlash from principals, teachers and some parent groups. The United Federation of Teachers, which represents the city’s teachers, laid out a safety plan last week that called on the city to provide a nurse for every school and to test every teacher, student and staff member who would enter a school building. The union said its teachers would strike if the city did not meet their demands. There are also concerns about whether buildings are properly ventilated.

Neither the teachers union nor the union that represents the city’s school principals and administrators were receptive to the mayor’s outdoor classroom initiative.

“The shortsighted guidance on outdoor learning also lacks detail, raising serious concerns around safety and security,” said Mark Cannizzaro, president the Council of School Supervisors and Administrators. “Furthermore, without funding, this plan will exacerbate already existing disparities.”

The council has urged the city to push back the Sept. 10 start date, saying there is not sufficient time to plan to reopen schools in the midst of a pandemic.

Many people have also been watching with trepidation as schools in Georgia, Florida, Mississippi, Tennessee and Indiana have been forced to shutter when staffers or students tested positive for the coronavirus. Some state and school leaders appear to have succumbed to pressure from President Trump, who sought to reopen schools as a way to restart the economy and boost his chances of reelection.

De Blasio has sought to distinguish New York City from those places, citing its progress in containing the pandemic. The city is faring far better than districts that have reopened in Georgia and Florida, states that now have some of the most severe outbreaks in the country.

Anthony S. Fauci, the nation’s chief infectious-disease expert, has endorsed the idea of holding schools outdoors to cut down on the risk of transmission among students. He has said schools should be doing their best to return children back to school safely, citing the enormous benefits to children being in school.

“I’ve spoken to superintendents and principals and recommend, if possible, outdoors, better than indoors,” Fauci said in an interview with The Washington Post this month.