There could be a big shake-up later to the way the government is run.
MPs are holding a vote on whether or not to change the way the House of Lords works.
The Deputy Prime Minister Nick Clegg wants to cut the number of Lords and change the way that they're appointed.
Unlike MPs, Lords aren't voted in by the public but they still get to make decisions on any new laws which are put forward.
The government wants four-fifths of members of a reformed House of Lords to be elected.
But not everyone is in favour of the changes. Lots of MPs think that the House of Lords works fine as it is.
It's expected that the government will win the vote to reform the House of Lords.
But even if they do win it, the changes still may not happen.
There had been a plan for MPs to vote on a timetable for the reforms but that has been cancelled.