This document was written by America's Frontline Doctors to address the issues with mandated mask wearing. All references in the letter are provided, and when possible PDF download links are also provided.
You can download the latest version of this document at their website using the links below. America's Frontline Doctors Letter (original source): https://americasfrontlinedoctors.org/wp-content/uploads/2021/07/6076ddcb96c12c1e6e611614_Mask-Public-Letter-Adult-1.pdf America's Frontline Doctors page with additional mask documents: https://americasfrontlinedoctors.org/legal/masks-the-law/
Masks are ineffective and in many ways they harm.