Is there a law in the book to protect the older, sick worker in Washington State?

My brother, 60 Asian works for a small bakery company owned by French boss for almost 30 years. Recently he got mild stroke at work short hospitalized and still trying to recover while going back to work. At work his boss push him to work harder than before he got sick; in my brother opinion his boss want to get rid of him, by pushing him to make some stupid move by walking out. Is there any law or lawyer deal with this kind of boss and protect this kind of worker? Provide any source is really appreciated.