La Leche League International has the following document:
You Can't Call Me for Jury Duty—I'm Breastfeeding
Washington State
RCW 2.36.100 stipulates that ".no person may be excused from jury service by the court except upon a showing of undue hardship, extreme inconvenience, public necessity, or any reason deemed sufficient by the court for a period of time the court deems necessary." The law does not specifically grant an excuse for a breastfeeding mother, but if she can show undue hardship or extreme inconvenience, service may be excused or postponed, depending on the needs of the court.
Jury summons received by mail should have a section that may be filled out detailing why jury service would constitute undue hardship or extreme inconvenience. The mother's particular situation should be explained and the form returned as directed. Most courts will accommodate the needs and desires of a breastfeeding mother. For example, the Thurston County Courts provide a private space for mothers serving on jury duty to express breast milk if they decide to participate. They have also granted many postponements for breastfeeding mothers. It is best to contact the courts as soon as a summons is received to learn what the particular policies are. Many areas allow individuals to postpone only one time.