While there are examples of such discrimination on sites with zero credibility, there are only a few seriously documented isolated cases of banks and credit card companies refusing to do business with people over the political views, trivial numbers versus the millions of customers out there. Banks and credit card companies don't know most customers political views.
However, while it's illegal to discriminate over employees political activities, it's not illegal for private businesses to discriminate over customers political views in most states in the US.
It's not something 99.99% of us need to be concerned over...