My guess is most teachers don't know that any union situation beyond the one in which they inhabit exists. In other words, in California most teachers have probably never even heard of Right To Work states, where teachers don't have to join unions or pay to support them.
I got the following information at last week's Concerned Educators Against Forced Unionism conference. I don't know how current it is, but it's a good place to start.
Model 1: Mandatory, monopoly, and compulsory exclusive bargaining for unions
District of Columbia
Indiana (somehow, also part of Model 2)
Maryland (somehow, also part of Model 2)
Model 2: Mandatory monopoly exclusive bargaining without compulsory unionism
Indiana (see also Model 1)
Iowa (a Right to Work, or RTW, state)
Maryland (see also Model 1)
South Dakota (RTW)
Model 3: No mandatory bargaining statute, but bargaining is not illegal and does occur at the will of the local school board
West Virginia (RTW)
Model 4: Collective bargaining is illegal or not accepted
North Carolina (RTW)
South Carolina (RTW)
I found that list to be a tremendous eye-opener with regards to the possibilities of a future without compulsory unionism.