When immigrants came to the US in the late 1800s and early 1900s, they typically got the worst jobs around.  They worked in difficult conditions doing unskilled labor.  Naturally, they were not paid much. 

The fact that they were not paid much is what impacted their housing and living conditions.  Because they were rather poor, they could only afford to live in cramped and often unsanitary conditions.  It was for people like these that the infamous tenements of places like New York City were built.  Immigrants would live crowded into small dark apartments that had no plumbing.  This was all that was available to them given how little money they could make doing the sorts of jobs they could get.