History Minute (066): Treatment of Black Soldiers in the North's army during the Civil War

Quoting Zinn:

What happened to blacks in the Union army and in the northern cities during the war gave some hint of how limited the emancipation would be, even with full victory over the Confederacy. Off-duty black soldiers were attacked in northern cities, as in Zanesville, Ohio, in February 1864, where cries were heard to “kill the nigger.” Black soldiers were used for the heaviest and dirtiest work, digging trenches, hauling logs and cannon, loading ammunition, digging wells for white regiments. White privates received $13 a month; Negro privates received $10 a month. 

Late in the war, a black sergeant of the Third South Carolina Volunteers, William Walker, marched his company to his captain’s tent and ordered them to stack arms and resign from the army as a protest against what he considered a breach of contract, because of unequal pay. He was court-martialed and shot for mutiny. Finally, in June 1864, Congress passed a law granting equal pay to Negro soldiers.

Excerpt From A People's History of the United States 

Howard Zinn