Wash. Rev. Code § 9.41.115
Notwithstanding the penalty provisions in this chapter, any person knowingly violating RCW 9.41.113 is guilty of a gross misdemeanor punishable under chapter 9A.20 RCW. If a person previously has been found guilty under this section, then the person is guilty of a class C felony punishable under chapter 9A.20 RCW for each subsequent knowing violation of RCW 9.41.113. A person is guilty of a separate offense for each and every gun sold or transferred without complying with the background check requirements of RCW 9.41.113. It is an affirmative defense to any prosecution brought under this section that the sale or transfer satisfied one of the exceptions in RCW 9.41.113(4).
RCW 9.41.115
Finding- 2015 c 1 (Initiative Measure No. 594): See note following RCW 9.41.010.