Facts: In a 1962 bond using the Port Authority of NY and NJ promised bondholders that certain revenues pledged as security for the bonds would not be used to finance unprofitable passenger railroad systems in the future. In 1974, NY and NJ retroactively repealed this covenant, so that the pledged revenues could be used to improve rail services. US Trust, one of the bondholders, sued on the grounds that the repeal violated the contractual clause.