In an article in Salon based on their  paper published in the American Journal of Political Science, "Labor Unions and White Racial Politics," Paul Frymer and Jake Grumbach discuss their finding that union membership reduces racial resentment toward African Americans. 

I think the labor movement has been kind of lost since basically the late 1960s as an organizer of change that intersects class and race. The unions didn't engage in this enough for many decades, and the unions had a lot of their own discrimination problems for many decades. But certainly, since the 1990s and in the 2000s, labor is really one of the largest, if not the largest civil rights organization in the country, and that needs to be recognized. More unions need to promote that and progressives need to recognize it. -- Paul Frymer, Professor of Politics and CSDP faculty associate, Princeton University

[Grumbach] pointed to his family background, telling Salon that his maternal grandfather 'was the editor of the Chicago Defender, a prominent black newspaper, and was really interested in and would report on the fights to integrate labor unions, and really saw an interracial labor movement as the key to civil rights and key to economic progress.' -- Jacob Grumbach, Assistant Professor of Political Science, University of Washington and 2018-2019 CSDP Fellow, Princeton University