Speculation has been mounting that the Crewe to Manchester leg may be scrapped to save money.
PM Rishi Sunak and Chancellor Jeremy Hunt will decide the next step this week.
The line to Leeds has already been axed, as has the Euston terminal in favour of a station outside central London.
Phase One, from London to Birmingham, has so far cost £23billion with more almost certainly needed.
Defence Secretary Grant Shapps said: “We do have to respond to the budgets.
“We’ve not only been hit by the coronavirus, but the war in Ukraine . . . with all of the consequences, all of the costs, and all the inflation.”
He said it would be “irresponsible” and “crazy” not to consider savings.
Greater Manchester Mayor Andy Burnham said axing the Crewe to Manchester leg would be treating northern voters as “second class citizens”.
He added: “It is a recipe for the North-South divide to become a North-South chasm.”
Labour tied itself in knots over HS2 last week, seemingly taking three different positions.
Shadow Chief Secretary Darren Jones said yesterday that the party would “love to see” it completed in full.