Antonyms for the phrase "gives green light" include "disapprove," "prohibit," "reject," "forbid," "veto," and "oppose." These antonyms imply a lack of support or authorization for a particular action or decision. When someone disapproves or rejects a proposal, they indicate that they do not agree with it or believe it is not the right course of action. Similarly, when someone prohibits or forbids something, they indicate that it is not allowed. Vetoing a decision means that it cannot be implemented or carried out. Opposing a proposal indicates that the person is against it and will work to prevent it from being put into place.