The mandate was announced by Gov. Jay Inslee last week during his first address since August when he announced state, health care, K-12 and higher education employees must be vaccinated by Oct. 18 or face losing their jobs.
The new mandate is similar to the outdoor mask requirements for large public gatherings recently implemented by King and Pierce counties.
A statewide indoor mask mandate, regardless of vaccination status, has been in place in Washington since Aug. 23.
Though outdoor events are generally considered to be lower risk for COVID-19 transmission, five outdoor superspreader events infected more than 500 people at concerts, fairs and rodeos across Washington, including an outbreak at the Watershed Music Festival, according to Washington State Secretary of Health Dr. Umair Shah.
The outdoor mask mandate comes as Washington state's hospitalization rates are at the highest level ever during the pandemic, according to state data. The Washington State Department of Health is encouraging hospitals to "limit and curtail elective procedures" in order to maintain enough capacity, Shah said.
The mandate, according to Inslee, can be enforced through the Washington State Department of Labor & Industries.
A webpage dedicated to mask policy on the Washington Department of Health website said there could be potential fines, though it is unclear if they apply to indoor or outdoor mask requirements.
"We hope people will wear a face covering to protect the health of their friends and loved ones. However, not following the order may result in a misdemeanor subjecting the violator to a fine of up to $100 and/or up to 90 days in county jail," the online information said.