My understanding is that the NEA is not a union, it is a voluntary organization.
In California, teachers must join the CTA, but they can opt out of their union dues being used for any political purpose other than political lobbying that has a direct effect on their jobs, wages, benefits, etc.
The NEA calls itself a "Professional Organization" but it is a union, and in many states you must join in order to teach at a public school.
The NEA employs about 1,800 "Uniserv Directors" across the nation. These people run political operations and carry the NEA agenda in all 50 state capitols.
In its IRS forms from 1996 to 2001, the NEA reported expenditures of $0 for political activites.