The phrase "get green light" usually means to receive permission to do something or approval for a project or proposal. Some antonyms for this expression might include "get red light," which means being denied permission, or "get yellow light," which signifies caution or uncertainty. Other antonyms could include "halt," "prohibit," or "forbid," all of which would mean blocking or preventing something from moving forward. Additionally, antonyms for "get green light" might include phrases like "hit a wall," "run aground," or "come to a standstill," all of which suggest coming up against obstacles that prevent progress.