The US has awful labor laws...most states are "work at will" states meaning that they can fire you for just about anything except for a handful of discrimination categories (even those leave too much room for shady interpretations.) Do not resign!! You will be denied unemployment benefits!! Their pressure is a ruse to cheat you!! They need to document why they are firing you. If you are a good worker they are are wide open for a legal fight. Keep a notebook/journal every day of what the do to you (only the facts keep emotion out of it) then seek legal counsel!!