Right-wingers David Davis – whom the Prime Minister defeated for the party leadership – and Liam Fox – the former Defence Secretary, who resigned from his Cabinet over his links to a lobbyist – will be the leading lights for Conservative Voice.
While the group, made up also of members of the 2010 intake at Westminster, insists it will work "from inside the party and alongside the leadership", Mr Cameron is likely to see this as another challenge to the direction of his leadership in the run-up to the next General Election.
Last month, the PM was urged by one of his own backbenchers to show whether he was "man or mouse" on airport capacity while a Tory colleague branded him Nick Clegg's "chambermaid".
At the weekend, it emerged a Tory backbencher had been approached to run as a "stalking horse" candidate against Mr Cameron.
Meanwhile, London Mayor Boris Johnson has been accused of using his post-Olympics popularity bounce to manoeuvre against the premier.
Some Tories believe Mr Johnson could be a future challenger to the Prime Minister's leadership of the Conservative Party.