Easier. The mayor issues an ultimatum: Return to work on your regular shift beginning at midnight or be fired. If youa re too sick to come to work, you had better be in the hospital or bring a doctor's note. There are few jobs even in NYC where a 50 year old person with no marketable skills can make $75,000/yr.
it would take several months to hire and train people to operate the system. and all the while, you would have violence and vandalism of various parts of the system thwarting attempts to break the union. in addition, other unions would join them in wildcat strikes if they saw the TWU was going to be broken.
it won't work.