Read the following news report from18 December 2013

"High Court rules against NSW Government's electoral donation laws after union challenge

"The High Court has upheld a union challenge to the New South Wales Government's electoral donation laws. In February 2012, the O'Farrell Government banned political donations from groups unless the donor is an individual enrolled to vote. Unions NSW launched a challenge to the laws, arguing that donations are a form of political freedom and that a ban is unconstitutional. In a unanimous decision, the High Court has found that the laws are invalid because they are contrary to the Commonwealth constitution."

This is an example of what feature in the Australian Constitution?