EPA had planned to issue the final standards late last month after several delays but again held back as White House review continues.
EPA is considering a standard between 60 and 70 parts per billion.
“Setting a health-based ozone standard based on the science is long overdue. We urge you to act today and set a new ozone standard to protect public health,” the letter states.
Business groups call the planned rules a costly overreach that will hurt the economy and job growth.