Tube strikes make the unions pretty unpopular.
What if the unions instead had a (publicised) day of turning a blind eye to fare-dodgers? That would still cost their employers plenty of money, but would presumably fill the public with enthusiasm rather than hatred.
The main problem would be that while there’s plenty of legal protection for strikes, there’s much less for employees refusing to perform some part of their job. Doubly so since London Underground undoubtedly already has disciplinary procedures in place for staff who help fare-dodgers. Also I’d imagine many tube employees not being too keen on people who don’t pay.
Still, it’d be a nice change from strikes. Have any transport unions tried this kind of thing, elsewhere in the world? What was the result?