The Supreme Court has, however, repeatedly recognized:
Elementary considerations of fairness dictate that individualsThere are also, however, decisions that have been found to be retroactive. See, Kay, Retroactivity and Prospectivity of Judgements in American Law, 62 Am. J. Comp. L. 37 (2014) (discussing case law).
should have an opportunity to know what the law is and
to conform their conduct accordingly; settled expectations
should not be lightly disrupted. For that reason, the principle
that the legal effect of conduct should ordinarily be
assessed under the law that existed when the conduct took
place has timeless and universal appeal. Landgraf v. USI Fim Prods.511 U.S. 244, 265-266 (1994), quoting, Kaiser Aluminum and Chemical Corp. v. Bonjorno, 494 U.S. 827, 855 (Scalia, concurring).
I was recently interviewed by the Washington Times about the issue and was quoted as explaining:
“In my view, it’s very unlikely that there will be any retroactivity with respect to this decision, and the reason for that is the Janus decision overruled 41-year-old precedent,” said Mitchell Rubinstein, a New York-based lawyer. “It changed existing law.” Alex Swoyer, In Wake of Supreme Court's anti-union ruling, non-members seek repayment of dues, Washington Times, August 12, 2018.
If the ruling is retroactive then how far back can courts go? The answer is that it depends on the applicable statute of limitations. Most of these cases are brought as 42 U.S.C. 1983 lawsuits which, in states such as New York, have a 3 year statute of limitations.
A finding of retroactivity can be devasting to some unions. That is why it is likely that most unions will seek to avoid litigation and settle cases involving individual union members or involving small numbers of employees. Class action lawsuits, however, may be a different story and only time can tell what will ultimately happen.