I am the editor, not the author of the article that you commented upon. However, I feel compelled to answer your question, nonetheless.

He is referring to contractual employees when using the term, casual labor. Of course, these employees are often procured by firms through an intermediary, such as a temporary service.

The workers are often offered no benefits, and the workers enjoy no job security. More and more labor in America is being reduced to this status, where they feel as outsiders and lack the peace of mind that accompanies benefits such as health insurance, pensions, and so forth.

Best,
Russell Cole