The Greens’ justice spokesman, David Shoebridge, said the opinion from constitutional attorney Patrick Keyzer prepared the path for new federal laws as the minority party intensifies its push to legalize marijuana ahead of a planned private member’s bill to be tabled next year. According to the advice, there are three Commonwealth heads of authority that might be used to legalize and control cannabis usage, with section 51’s provision relating to copyrights, patents for new discoveries and designs, and trademarks providing the most direct route.