The actor wrote a letter to the court calling Williams a generous man who dedicated his life to empowering workers and fighting inequality. Glover, 74, cited his experience working with Williams as the union conducted a failed effort to organize Nissan Motor Co. workers in Mississippi.
U.S. District Judge Paul Borman last week sentenced Williams to 21 months in prison, a little less than the two years prosecutors asked for.
"There has been no one that I have seen put themselves in the frontlines of the union struggle and with such generosity and openness as Dennis Williams," wrote Glover, who identified himself at the end of the letter as an actor and humanitarian. "The idea of service has been a hallmark of Dennis's career, always using his platform to represent a just world for workers and helping to build the UAW as one of the most important unions in the world."