Ultra Vires being some fancy latin term for the gov't not really having the power to make the law as it infringes on either another section of government's power/area of control, or infringes on higher legislation like constitutional rights and freedoms. For instance in Canada the Federal Gov't cannot pass legislation on healthcare or education as that is under the jurisdiction of the Provincial gov't. The federal gov't could not pass a curfew law requiring people to be in their homes before midnight and have it up held in court without invoking the not withstanding clause of the Canadian Charter of Rights and Freedoms to allow the law to ignore our right to freedom of movement guaranteed in the Charter.