The U.S. Open cut line is set after two rounds, with a cut rule determining the weekend field that is slightly different from what you see week-to-week on the PGA Tour.
The U.S. Open cut rule is among the strictest in the majors, determined by allowing only the top 60 players and ties getting into the final two rounds. There is no 10-Shot Rule, which means there's no guarantee that a player within 10 shots of the lead qualifies for the weekend rounds. There is a 10-shot rule at the Masters. There also isn't the possibility of a 54-hole cut.
The U.S. Open cut rule doesn't account for a difference between professionals and amateurs. They're treated the same by the U.S. Golf Association.