government contractor immunity

if this authority to carry out the project was validly conferred, that is, if what was done was within the constitutional power of Congress, there is no liability on the part of the contractor for executing its will. Where an agent or officer of the Government purporting to act on its behalf has been held to be liable for his conduct causing injury to another, the ground of liability has been found to be either that he exceeded his authority or that it was not validly conferred.