Tory Michael Fabricant said he knew between 80 to 100 of his fellow MPs have "really serious doubts" about HS2, amid talk around 30 to 40 Conservatives will vote against the Government in the Commons today.
But the Lichfield Tory said several MPs were reluctant to "use up our stocks" with party enforcers when the project is expected to clear its second reading thanks to support from Labour.
The HS2 link between London, the Midlands and the North of England is expected to cost £42.6bn, which includes including contingencies, with £7.5bn for the trains.
Mr Fabricant is among the senior Tories who have tabled amendments in an attempt to block the Government's plans.
He wants the coalition to bring forward a cheaper and more environmentally "sympathetic" route and has warned the line as set out in the High Speed Rail (London-West Midlands) Bill is "significantly more costly" than it need be to reduce damage to the environment.
Speaking on Murnaghan on Sky News, he said: "If Labour was against it the rebellion would be a lot bigger than 40. The government whips advised Number 10 that without Labour support, the legislation wouldn't get through. And I believe from all the consultations that if Labour wasn't supporting it the legislation wouldn't go through."