AS, AD, and the New Deal
Even staying within the AD-AS model, it seems possible to argue the opposite point of view. Imagine you are a manager of a firm considering a long-term investment project. The President has just announced a policy to encourage your workers to form a cartel. How does that influence your decision to proceed with the project? Very likely, it deters you. Investment spending, however, is part of aggregate demand (in fact, one of the most volatile components). Thus, the policy could shift the AD curve, as well as the AS curve, in a contractionary direction.
As a general matter, the state of aggregate demand depends on an amorphous variable called confidence. Anything that threatens to screw up AS in the long run most likely reduces confidence and AD in the short run. The textbook separation of AD and AS is useful for focusing discussion in the undergraduate classroom, but events in the real world are rarely so clean.