During the January 9, 2006, party leaders' debate for the 2006 federal election, Prime Minister Paul Martin unexpectedly pledged that his Liberal government, if returned, would support a constitutional amendment to prevent the federal government from invoking section 33, and challenged Conservative leader Stephen Harper to agree. This sparked a debate as to how the notwithstanding clause can be amended. Some argued that the amending formula required the federal government to gain the approval of at least seven provinces with at least half the national population (the standard procedure). Others argued that since the proposal would only limit the federal Parliament's powers, Parliament could make the change alone.