Update: An email response from Maxford Nelsen Director of  Labor Policy | Freedom Foundation

“First, it’s still a bit too early to conclude that public-sector union membership has not declined in the wake of the Janus decision. In many cases, the data is either unavailable or still very preliminary. Unions made similar claims in the months after the U.S. Supreme Court’s 2014 decision in Harris v. Quinn, which made union dues payment optional for “partial-public employees.” Four years later, however, the two biggest unions in Washington state affected by that decision have seen the percentage of people in the bargaining unit paying them decline from 100 percent to 75 and 36 percent, respectively, according to state payroll data. See https://www.freedomfoundation.com/labor/seiu-775-membership-drops-after-freedom-foundation-litigation/

“Second, unions have employed a range of tactics designed to make it difficult for public employees to cancel the deduction of union dues from their wages. Many major unions revised the terms of their membership forms in the years leading up to Janus, inserting “irrevocability” provisions that limit the time period the signer can cancel the deduction of dues from their wages to a narrow annual window period as short as seven days. In short, the number of public employees who have successfully canceled the deduction of union dues from their wages since Janus is significantly smaller than the number who have attempted to cancel such deductions. Challenging the validity of these schemes in court could take some time.”