Senior military army officers have criticised General Sir Richard Dannatt's recruitment as military adviser to the Conservatives.
The former head of the Army will join Parliament as a Tory peer before potentially becoming a junior defence minister under a future Conservative government.
The Guardian reported that senior Conservative frontbenchers have lodged complaints after the leadership failed to consult them on the appointment.
Meanwhile, Lord Guthrie, a former chief of the defence staff, told the Independent that General Dannatt should not accept the offer.
He said: "If he is going to the House of Lords, it's best to be a crossbencher. I will give advice to anyone, Labour or Conservative, but I wouldn't want to be associated with any one political party."
There have been concerns that the prospect of General Dannatt becoming a Tory minister could mean politicising the Army at a time when it needs broader support.
And worries in the Ministry of Defence centre on the effect of General Dannatt's appointment on the working relationship between serving commanders and ministers.
Another reason for the backlash has been that General Dannatt is still on the Army payroll and has recently accepted the position of constable of the Tower of London, a Crown appointment which is historically non-political.
Shadow foreign secretary William Hague insisted that the general would be an asset to the party, providing advice on war.
And shadow defence secretary Liam Fox said: "It's not a crime to bring weight and experience into government with you, and I very much welcome Richard Dannatt as a member advising my team."
However, Lord Guthrie said: "On a broader basis, this is not good for the Army. It would now be easy to paint the criticisms he made about Afghanistan as political, and that is not fair on others who have also tried to get better resources for our forces."
Ministers have attacked the appointment, which came after General Dannatt said in the summer that he was not acting for party-political reasons.
Immigration minister Phil Woolas called the move a "stunt by the Conservative Party".
