From Guns.com:

However, before the ink is dry on the prohibition, the Firearms Policy Coalition issued a call for potential plaintiffs from among Washington residents that could be impacted by the ban. 

“By enacting the unconstitutional SB 5078, the State of Washington has further restricted the fundamental human rights of Washington residents and visitors by banning the transfer and other conduct related to so-called ‘large capacity’ magazines,” said the group in a statement. “FPC condemns this latest act of state aggression and will not allow this law to go unchallenged. To that end, FPC Law will be taking aggressive action to fight this immoral law and seek to have it enjoined and declared unconstitutional.”