Antonyms for "gave the green light" could include phrases such as "denied permission," "disapproved," or "vetoed." Similar phrases like "put the brakes on" or "halted progress" also convey the opposite of giving approval for a project or plan. Other antonyms might include "objected," "opposed," or "thwarted," each conveying a sense of actively preventing something from moving forward. Overall, the antonyms for "gave the green light" imply a sense of refusal or reluctance, preserving the sense of a decision being made, but in the negative.