Unlike their predecessors, the Imperium Senate actually had a part in making laws in the Imperium. Made up of Senators from each of the member worlds of the Imperium as well as some from systems considering becoming members, the Senate both introduced laws and had the power to veto laws introduced by the Grand Commander.
They also possessed nominal control over the military, unlike in the Eriaduan Empire in which control was only with the Senate in theory. They closely advise the Grand Commander on the running of the Imperium and its expenditures. Also, should the Grand Commander derelict his duties in anyway, the Senate had the power to replace him, though they had to have a majority vote and it also had to be confirmed by the Order of Judges.