The Commonwealth Government will deliver its budget today, but legal experts have raised questions about how key aspects will be passed through parliament. For example, the opposition parties have signalled their intention to block the government’s climate change policies, and in response Environment Minister Greg Hunt suggested he would include them as part of the budget. As professor Anne Twomey explains, constitutional rules about how the Senate deals with appropriation bills could lead to a crisis if neither side backed down. Similarly, the Clerk of the Senate, Rosemary Laing, said that including a new “deficit levy” in a supply bill would be legally problematic, as the constitution requires supply and taxation to be dealt with in separate bills. However, these remain hypothetical problems until the budget bills are revealed.