The NYT had a good piece highlighting new research by Gabriel Zucman, Thomas Torslov, and Ludvig Wier indicating that multinationals may be shifting as much as 40 percent of their profits to tax havens. This is a pretty serious problem if we actually expect companies to pay their taxes.
As I have pointed in the past, there is actually a very simple mechanism that would pretty much block this sort of tax avoidance. If companies were required to give the government non-voting shares in an amount equal to the targeted tax rate, then it would be virtually impossible for them to escape their income tax liability without also defrauding their shareholders. But I realize this is probably too simple to be taken seriously.