Kreidler told the insurers they are not required to cover sexual reassignment surgery, but they do have to give transgender people the same access to health care as everyone else.
The insurance commissioner notes if services are covered for others, such as hormone therapy or breast reconstruction, they have to be covered for transgender people.
He notes that many Washington employers have already taken action to prevent discrimination against transgender people on their payroll. Medicare recently lifted a ban on coverage for sex reassignment.
Kreidler says his office is reviewing all 2015 individual and small employer health plans to look for discriminatory exclusions.