Why was Fred Tayama badly beaten?

Tayama is beaten because of his cordial relations with the Administration, and his refusal to support the Kitchen Workers' Union. Thus, his beating was set up to make a point about coming rebellion.

This was a young cook well known for his defiance and contempt for the authorities. He had been trying to organize a Kitchen Workers’ Union and had recently charged the camp’s chief steward, a Caucasian, with stealing sugar and meat from the warehouses to sell on the black market. Since sugar and meat were both in short supply, and since it was rumored that infants had died from saccharin mixed into formulas as a sugar substitute, these charges were widely believed.