The chart shows that the income of the very rich (the so called "top 1%") falls as trade union membership rises and increases when trade union membership falls.
Unions are stronger when they have more members. When they have more members then their bargaining position with employers is stronger. Therefore, they can make sure that their members get better wages and a fairer share of the wealth.
If the unions have lower numbers of members then they are not in such a strong bargaining position with employers and wages are reduced while the income of senior management and rich shareholders rocket upwards.
So encouraging trade unions rather than attacking them is not only about democracy and human rights but also about fairness and equality.
Hat tip Ravi S.