No. The city might terminate any contract you held with them if they found out you were a member but that's about all they could do alone.
The holy grail is to get the NRA listed as a terrorist organization at the federal level, which might well place members in legal jeopardy, even subject to arrest in a declared emergency. They couldn't actually do much with 5 million people but might do very well against, say, Board members and Life and Endowment members. Enough to frighten the rest into submission, or so goes the assumption.
Yes, it's unconstitutional as hell to do any of this, which is why the NRA is suing the city. This isn't simply empty posturing, it's class warfare with real consequences to the victims, and the city government is well aware of that, and will do whatever the courts will let them get away with in order to prosecute it. And that includes packing the Supreme Court at the federal level, after which justice becomes whatever they say it is. The courts need to nip this one in the bud because it's a very clear path to civil war.
Hear! Hear!
Spot on, Bill! Spot on!
Taxman Bravo Zulu!