Antonyms for the phrase "giving the green light" could include "prohibiting," "forbidding," "blocking," "denying," "refusing," or "restraining." These words suggest the opposite of granting approval or permission, instead indicating a sense of restriction, limitation, or rejection. While "giving the green light" implies a sense of support or encouragement, these antonyms convey a more negative or critical attitude. Depending on the context, using these antonyms could suggest a more cautious or hesitant approach, or indicate a lack of agreement or consensus among different parties. Ultimately, the choice of antonym will depend on the specific situation and intended message.