From the Department of No Sh** Sherlock:
Think Progress: The middle class brings home a substantially larger share of aggregate earnings in states that have high rates of union membership than in those where fewer workers are organized, a Center for American Progress Action Fund (CAPAF) analysis of Census data shows. Amid very high and still increasing income inequality, union density appears to offer some buffer for middle-class Americans. [...]
...CAPAF’s David Madland and Keith Miller found that the states with the lowest rates of union membership return below-average shares of income to their middle-class residents. [...]
The rise of inequality over the past three decades tracks closely with the decline of union membership.
The income of the richest one percent has risen as middle class incomes drop.
As TP points out, and as we have in many posts, as unions get stronger, they increase their ability to stand up for workers. When that happens, not only does it improve work place conditions, but in the long run, income inequality is reduced.
And since the very rich make way more than the rest of us, leveling the playing field benefits the entire country, the health and welfare of more Americans, and the economy.
Not to mention, the decline of organized labor has helped worsen racial wage gap.
While you're at it, check out "What a difference a union can make!" and "Why unions matter, in a measly 1 minute 19 seconds."