The unnamed ministers want Cameron to abandon the ministerial code, which requires collective responsibility among ministers, so that they can campaign for Brexit.
The ministerial code, changed this year after the Conservatives won a majority at the General Election, says: "Ministers also have an obligation to ensure decisions agreed in Cabinet and Cabinet Committees (and in write-rounds) are implemented."
A cabinet source told the Daily Mail ministers who want to campaign to leave the EU will be sacked. The minister added:
The idea that the Prime Minister will welcome back people who have spent the previous few months waging a campaign against him is a joke. If people want to campaign to leave then they will be out – it is just a matter of timing.
Meanwhile, one minister told The Telegraph it would be “insane” for Cameron to expect europsceptic ministers to campaign for Britain to remain in the EU, while another said it would result in a "bitterly divided party".
In public Cameron has maintained that he hasn't yet made a decision on whether or not to let ministers campaign with their conscience.
The Prime Minister has committed to holding an In/Out EU referendum before the end of 2017, and has said if he gets the reforms he seeks he will campaign to remain a member of the EU.
Cameron will announce a full list of his demands in November.