Start digging the trenches. Labour has signalled that it won't support a timetable ("guillotine") motion to ensure the passage of the government's bill to reform the House of Lords - which means the bill may never get out of the House of Commons.
Ed Miliband has announced his party is "serious" about Lords reform, and will therefore support the bill at second reading, and seek to amend it thereafter. But, he argues, the bill is far too important to have debate curtailed by a guillotine, and so it will oppose the timetable motion.
This is close to a death blow to the bill. Tory backbenchers who oppose Lords reform, either on constitutional grounds, or because they just want to slap Nick Clegg, seem certain to oppose the timetable motion in sufficient numbers to ensure that they plus Labour will be able to outvote the government.
And without a timetable motion the debates at committee stage, which will be taken on the floor of the Commons, will just grind on and on and on and on and on and...
Other legislation may be crowded out, the Tory whips will face the unpalatable job of trying to force their backbenchers through the lobbies in the cause of coalition unity, and tempers will undoubtedly fray.
Which, I suspect, is why Labour have really chosen to oppose any guillotine motion. To be sure, there is plenty to debate - who sits in parliament for how long, what their powers should be, whether a new look Upper House would have to be approved by the voters in a referendum, and much, much more. But Labour used the guillotine on any number of major constitutional measures when it was in office - so the sudden concern for proper parliamentary scrutiny now looks a little suspect.
It's hard to avoid the suspicion that their main objective is to maximise the grief that this will cause in the coalition, as Lib Dems and Tories slug it out for 20 days or more.
It may be that Labour and Tory rebels manage to defeat this programme motion, but face another, later on. And, who knows, maybe after an exhausting couple of weeks of wall-to-wall committee stage debates, a second programme motion might seem more attractive… But anyone who's watched the Tory awkward squad in action should be in no doubt about their ability to keep talking, pretty much for ever. They are unlikely to falter. The question is: will Labour? Might the coalition offer them concessions over a possible referendum on the changes, and on their other gripes about the bill? If Lords Reform clears the Commons, it can be imposed, even if the Lords reject it. But that has just become much more difficult to achieve - and that could mean more coalition infighting as the Lib Dems strike back.