Prime Minister Theresa May is facing a potential backbench rebellion over potential defence cost-saving plans.
Tory MP Johnny Mercer, a former Army officer who now sits on the Defence Select Committee, told Sky News he has "a resilient cohort of Conservative MPs" who are unhappy with the idea of further cuts.
He was speaking after The Times reported that Defence Minister Tobias Ellwood had told colleagues of his "deep discomfort" about the levels of cuts facing the Ministry of Defence (MoD).
The newspaper claimed the planned cuts would see the Army lose 12,000 soldiers, leaving its full-time strength at just 70,000.
Other possible cuts were thought to include reducing the order for Ajax armoured vehicles, delaying tank upgrades, axing amphibious assault ships HMS Albion and HMS Bulwark, and the loss of 1,000 Royal Marines.
With the Government's small majority only seven, Tory MPs would need to rebel in any potential vote to defeat any legislation.
Mr Mercer said: "It is the first duty of government. We know we're in difficult times but we can't just talk about it we have to fund it properly, we have to resource it properly.
"What do we want from the military? You can't just talk about that. You have to fund it properly, you can't ask them for stuff and then not give them the money to do it.
"There was clearly some fat in the system, but we've hit a resilient boulder and it's our job as politicians to stand up for that and to stand up for what we believe in."
The newly-appointed Defence Secretary Gavin Williamson is also reportedly unhappy with the level of cuts his department may face.
Defence minister Mr Ellwood served in the Royal Green Jackets from 1991 to 1996, with tours in Northern Ireland, Cyprus, Kuwait, Germany, Gibraltar and Bosnia.
He is reportedly prepared to resign if the cuts are given the green light.
The Bournemouth East MP is now in the Army Reserve and bravely tried to save the life of police officer Keith Palmer, who was stabbed by a terrorist outside the Palace of Westminster in March.
Fellow Tory MP Tom Tugendhat, chair of the Foreign Affairs Committee, tweeted his support for Mr Ellwood saying he was "proud" of his stance.
An MoD spokesman said: "We have the biggest defence budget in Europe and are one of very few countries to not only meet but exceed NATO's 2% spending target.
"In the face of intensifying threats, we are contributing to the cross-government review of national security capabilities and looking at how we best spend the rising defence budget to protect our country.
"No decisions have been made and any discussion of the options is pure speculation."