You should note that the tax proposals were made by American politicians, so this isn't a unfair treatment by the global market, but the effect of the Robin hood style act proposed by the senators involved; Bernie Sanders, Ed Markey, and Kirsten Gillibrand and could likely be a public front to support their political agendas.
This is not indicative of any prejudice towards American billionaires (which is ranked no.1 on the
list) or a more receptive economic environment for the rich in other countries, we actually have a high number on the rich list leaving China and other areas with high political manipulation of the nation's market.
Tax hikes also affects a bulk of the population and unionization helps protects the workers in cooperations, reason why some work houses are set up in areas where labour is cheap. Rather than seeing this as an attack, I think it should be established in many more countries