A set of powerful voices, including the unions for New York City teachers and principals, have joined the growing chorus of educators saying they’re uneasy over the imminent reopening of the city’s public schools.

The president of the Council of School Supervisors and Administrators, representing 6,400 principals, sent a letter Wednesday to Mayor Bill de Blasio and Schools Chancellor Richard Carranza, questioning the lack of adequate planning and urging them to heed “dire warnings concerning the city’s September 10th reopening plan." The principals are calling on the de Blasio administration to delay the first day of school.

De Blasio has previously said he would like to see students back in school on September 10th, but no official first day of school has been announced.

Shortly after the CSA letter was released, the United Federation of Teachers union -- comprised of 200,000 members -- called for delaying the first day of school as well.

"The UFT has said repeatedly that we cannot re-open schools unless they are safe for students and staff. The principals union — whose members will be responsible for enforcing coronavirus safety protocols in the schools — now believes that school buildings will not be ready to open in September. We need both safety and sanity in this crisis,” said UFT President Michael Mulgrew in a statement. “Will any parents be willing to put their children in a school whose principal believes the building is not ready to open because it is not safe?"

At a press conference outside a middle school in Far Rockaway in Queens Wednesday, de Blasio said he hears the unions’ concerns and believes the next month will be enough time to prepare schools for reopening.

“We have been systematically addressing those concerns and we have a whole month 'til school opens and we're going to do a lot more,” de Blasio said, without committing to a set timeline. “So, I hear their concerns but this ballgame is far from over. We're going to make these schools safe.”

“The vast majority of our students are currently planning for blended learning, and we know our dedicated school leaders and educators will show up for them like they have every year,” said DOE spokesperson Danielle Filson in an email Wednesday.

De Blasio announced this week that more than 700,000 students may start the school year with some in-person instruction, based on a survey for enrollment. The city has the largest school district in the country with, about a million students expected to enroll this fall.

Mark Cannizzaro, president of the CSA, also criticized the de Blasio administration for waiting until August 6th to have their first meeting with the principals of the city’s 1,600 public schools to discuss individual school plans for blended learning schedules, and gave them four business days to submit the plans to the DOE.

“School leaders rose to that pressing challenge while also preparing to submit their programming model selection to the DOE by August 14th, which they have grappled with due to lack of information on student enrollment and teachers with accommodations to work remotely,” Cannizzaro said, pointing out “we are now less than one month away from the first day of school and still without sufficient answers to many of the important safety and instructional questions we’ve raised on behalf of school leaders and those they serve.”

But de Blasio said delaying school reopening is tantamount to delaying education: “My sense is if you want to take away another month of a kid's education, you could do that, but that's not where I start. I start with, let's answer the valid concerns that teachers and administrators are raising with a whole month to go,” he said at the press conference.

A group of principals of District 15 schools in Brooklyn also raised issues in a letter to Governor Andrew Cuomo, de Blasio and Carranza Tuesday, saying they are “gravely concerned that the central response to opening has been piecemeal.”

“Planning for such uncertainty is almost impossible without a clear long term blueprint for reopening, with coordinated guidance from the city and state education departments, and guided by public health experts,” said the letter, signed by three dozen principals of the district’s 49 schools.

Part of the problem with reopening schools in a month is the simple lack of supplies, from personal protective equipment to testing kits, critics said.

“We know that many schools are already purchasing tents, negotiating outdoor space with elected officials, and raising significant amounts of money to purchase PPE for staff and students,” the D15 principals wrote. “While we appreciate that school communities are actively seeking to solve these problems, we fear it will further the divide between the haves and have nots in our city."

The New York State Nurses Association also issued a statement Monday calling for postponing the reopening of city schools. “Bringing people together in enclosed spaces, without the robust public health infrastructure nurses have called for since the beginning of this pandemic, will undoubtedly increase the spread of the virus. Opening in-person schooling could easily erase the progress New York has made, and spark a resurgence of COVID-19,” the statement said.

With the unprecedented challenges, the school system should stop trying to meet deadlines and think differently, said one middle school principal who spoke on the Brian Lehrer Show Wednesday.

“Time does not have to be our enemy,” said Roshone Ault Lee, principal and founder of the South Bronx Academy for Applied Media. “It can actually be an ally. So if we delay the start of school and we're able to strategically plan and think through and mitigate all of the challenges, it will be beneficial for everyone.”