Background: Glover was born in San Francisco, the son of Carrie (Hunley) and James Glover. His parents, who worked as postal workers, were highly active in the National Association for the Advancement of Colored People (NAACP), working to advance equal rights. Glover's mother, daughter of a midwife, was born in Louisville, Georgia and graduated from Paine College in Augusta, Georgia. As an adolescent and a young adult, Glover suffered from epilepsy but has not suffered a seizure since age 35.
Context: While attending San Francisco State University (SFSU), Glover was a member of the Black Students' Union, which, along with the Third World Liberation Front and the American Federation of Teachers, collaborated in a five-month student-led strike to establish a Department of Black Studies. The strike was the longest student walkout in U.S. history. It helped create not only the first Department of Black Studies but also the first School of Ethnic Studies in the United States.  Hari Dillon, current president of the Vanguard Public Foundation, was a fellow striker at SFSU. Glover later co-chaired Vanguard's board. He is also a board member of the Algebra Project, the Black AIDS Institute, Walden House and Cheryl Byron's Something Positive Dance Group. He was charged with disorderly conduct and unlawful assembly after being arrested outside the Sudanese Embassy in Washington during a protest over Sudan's humanitarian crisis in Darfur.  In 1999, he used his leverage as a former San Francisco cab driver to raise awareness about African Americans being passed over for white passengers. In response, Rudolph Giuliani launched Operation Refusal, which suspended the licenses of cab drivers who favored white passengers over black ones.  Glover's long history of union activism includes support for the United Farm Workers, UNITE HERE, and numerous service unions. In March 2010, Glover supported 375 Union workers in Ohio by calling upon all actors at the 2010 Academy Awards to boycott Hugo Boss suits following announcement of Hugo Boss's decision to close a manufacturing plant in Ohio after a proposed pay decrease from $13 to $8.30 an hour was rejected by the Workers United Union.  On November 1, 2011, Glover spoke to the crowd at Occupy Oakland on the day before the Oakland General Strike where thousands of protestors shut down the Port of Oakland.
Question: What causes did he support?

Answer:
he used his leverage as a former San Francisco cab driver to raise awareness about African Americans being passed over for white passengers.