Opponents of the HS2 rail link are "putting our country's future at risk", Prime Minister David Cameron has said.
He spoke at the CBI annual conference after speculation that Labour would withdraw its support for the high-speed rail network from London to Birmingham, Manchester and Leeds.
Shadow chancellor Ed Balls will say Labour's support is "not at any cost".
Mr Cameron also said the new boss of HS2 would find ways to cut the estimated £50bn cost of the scheme.
He said Sir David Higgins would "make absolutely sure we drive every extra bit of cost out of this that we can, so it comes in under the budget that's been set".
"I want to make sure we get every penny of value for money from this HS2 investment," he said.
"I think it is fantastic that Sir David Higgins - the man who built the Olympics on time and on budget - is going to be running HS2."
He added: "People who are against it, in my view, are putting our country's future at risk, they are putting the future of the North of England at risk," he said.
"We need to have a concerted consensus across business, across politics, that we get behind these large infrastructure projects."
He said making the investment would "make sure our economy shares growth between the north and south - it will link eight of our 10 biggest cities".
Sir David has said he believes the scheme can come in "substantially" under the current budget if the £14bn set aside for contingency costs is reduced.
Mr Balls, meanwhile, told the conference: "The Labour Party cannot - and will not - give the government a blank cheque."
"That is what you would expect from any credible official opposition seeing a government desperately mismanaging a project. And that is what is happening here with the costs having shot up to £50bn.
"We will put the national interest and the taxpayer interest first.
"We will take a hard-headed look at the costs and benefits of the scheme to ensure this is the best way to spend £50bn for the future of our country."
He said a Labour government would set up an independent infrastructure commission to end delays in major infrastructure projects.
In his speech, CBI president Sir Mike Rake criticised "commercially harmful" indecision over HS2.
"We cannot have every major infrastructure decision continuously redebated at every turn, as we're seeing with HS2," he told the conference.
"Undoubtedly, a better effort should be made to communicate the benefits of high speed rail, and this must be positioned within an overall, long-term strategy of what the country needs across all modes of transport.
"Decisions have to be made, and once they have been made then we should stick to them."
MPs last week approved funding to prepare for the high-speed rail network.
The HS2 project would see lines built between Birmingham and London, followed by a V-shaped second phase building separate tracks from Birmingham to Manchester and Leeds.
The government hopes to begin construction on the first phase of HS2 in 2017 and open that part of the line in 2026.
The additional lines to Leeds and Manchester could then be completed by 2032-33.