Steinbeck in The Grapes of Wrath does present the wealthy and powerful abusing the poor every chance they get.  If you need a citation or quote, here's the most powerful one in the book.  It closes the novel.  It demonstrates the depths to which the poor have sunk, as well the lengths the poor are willing to go to, to help one another.

For a minute Rose of Sharon sat still in the whispering barn.  Then she hoisted her tired body up and drew the comfort about her.  She moved slowly to the corner and stood looking down at the wasted face, into the wide, frightened eyes.  Then slowly she lay down beside him.  He shook his head slowly from side to side.  Rose of Sharon loosened one side of the blanket and bared her breast.  "You got to," she said.  She squirmed closer and pulled his head close.  "There!" she said.  "There."  Her hand moved behind his head and supported it.  Her fingers moved gently in his hair.  She looked up and across the barn, and her lips came together and smiled mysteriously. 

This is one of the most poignant scenes in American literature.  I can't think of a better one to demonstrate what Steinbeck reveals about the end result of exploitation in Dust Bowl America.   

The Grapes of Wrath is a thorough examination of the repurcussions of The Great Depression on American society. In short, the quest for wealth and power only further corrupt the relations between the haves and have-nots within our society. One of the clearest expressions of this is when Steinbeck criticizes the money-hungry banks as "monsters" with an unquenchable thirst for cash. These banks continue to scheme and cheat individuals out of what is rightfully theirs in order to increase their profit margins. Similarly, tractors are viewed in much the same light as the machines allow banks and corporate farmers to devour more and more land running the family farms out of business.