The American Federation of Teachers (AFT) is raising concerns about new Centers for Disease Control and Prevention (CDC) guidance that reduces social distancing requirements in classrooms by 3 feet. 

In a letter addressed to CDC Director Rochelle Walensky and Education Secretary Miguel Cardona, AFT President Randi Weingarten wrote Tuesday that the organization was "not convinced" current evidence supports changing physical distancing restrictions. 

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"Our concern is that the cited studies do not identify the baseline mitigation strategies needed to support 3 feet of physical distancing. Moreover, they were not conducted in our nation’s highest-density and least-resourced schools, which have poor ventilation, crowding and other structural challenges," she said in the letter. 

Weingarten also stressed the importance of strengthened "layered mitigation" amidst these changes, including "universal and correct masking; effective ventilation; thorough cleaning of buildings; regular COVID-19 testing of teachers, staff and students; effective contact tracing and quarantine/isolation protocols; and the availability of vaccines to all people in schools who are eligible."

She also requested that the Department of Education release a national checklist outlining enhanced mitigation strategies and provide details in conjunction with the CDC about proper implementation and that the CDC conduct "comparative studies" on mitigation efforts in areas that do not have proper ventilation and have been "systematically under-resourced for decades."

"AFT members want to trust the CDC to keep all of us safe, and to trust the Education Department to have students’, families’ and educators’ well-being as its goal," Weingarten said. 

AFT told Fox News on Wednesday it had yet to receive a response. 

The nation's second-largest teachers' union represents 1.7 million members in more than 3,000 local affiliates nationwide, according to its website.

In this Sept. 3, 2020, file photo, students keep social distance as they walk to their classroom at Oak Terrace Elementary School in Highwood, Ill., part of the North Shore school district. New evidence that it may be safe for schools to seat students 3 feet apart — half of the previous recommended distance — could offer a way to return more of the nation’s children to classrooms with limited space. (AP Photo/Nam Y. Huh)

In this Sept. 3, 2020, file photo, students keep social distance as they walk to their classroom at Oak Terrace Elementary School in Highwood, Ill., part of the North Shore school district. New evidence that it may be safe for schools to seat students 3 feet apart — half of the previous recommended distance — could offer a way to return more of the nation’s children to classrooms with limited space. (AP Photo/Nam Y. Huh)

On Friday, the CDC announced the update, stating in a release that it now recommends students should maintain a distance of "at least 3 feet in classroom settings" with universal masking in elementary schools and areas where transmission is low, moderate or substantial.

In a distinction, the CDC added that middle school and high school students should be at least 6 feet apart in high-transmission areas if cohorting is not possible. 

The agency cited three studies published in Morbidity and Mortality Weekly Report (MMWR) last week that "build on evidence that physical distancing of at least 3 feet between students can safely be adopted in classroom settings where mask use is universal and other prevention measures are taken."

The CDC also continues to recommend at least 6 feet of distance in common areas, during activities when increased exhalation occurs, in community settings outside the classroom and when masks cannot be worn.

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Walensky said in the release that the CDC is committed to "leading with science and updating our guidance as new evidence emerges."

"Safe in-person instruction gives our kids access to critical social and mental health services that prepare them for the future, in addition to the education they need to succeed," she said. "These updated recommendations provide the evidence-based roadmap to help schools reopen safely, and remain open, for in-person instruction."

The agency had previously recommended that schools keep their students six feet apart -- with the exception of the lowest levels of transmission -- but many schools had a hard time bringing back students under that guidance. 

The move from the CDC is expected to allow more students to attended classes in person: a major goal for the Biden administration within its first 100 days in office and beyond.

Last week, the administration announced it would allocate $10 billion toward coronavirus screening tests for teachers, students and staff and there is $122 billion being sent to K-8 schools across the country from the $1.9 trillion American Rescue Plan.

On Wednesday, the administration is hosting its "National Safe School Reopening Summit" during which Cardona, educators and policymakers will discuss reopening at this stage of the pandemic.

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The push to reopen schools marks a shift from the administration's initially cautious approach as more and more Americans are vaccinated.

The CDC and Department of Education did not respond to Fox News' request for comment.