David Cameron has been asked to explain why he has referred culture secretary Jeremy Hunt to the Leveson inquiry and not the independent adviser on minister's interests.
Labour will call for the the prime minister to defend himself to MPs on Monday after he refused to launch inquiry into Hunt's alleged breach of the ministerial code.
The culture secretary has been accused of acting as a "cheerleader" for News Corporation's BSkyB takeover bid after the Leveson Inquiry published a raft of email exchanges between the company's chief lobbyist and Hunt's office.
Lord Justice Leveson has rebuffed Hunt's request to appear early so the issue will not be tackled in the inquiry until at least mid-May.
It is also thought Leveson will not rule on whether Hunt has broken the ministerial code in his dealings with Rupert Murdoch's company, adding pressure to Cameron to launch an official independent inquiry.
Labour have now insisted Cameron appears in parliament to personally explain why he is "trying to hide behind the Leveson inquiry".
"With parliament breaking up on Tuesday, Cameron must come to the Commons and explain to the British people why he is ducking his responsibilities to enforce the ministerial code," the party said.
But Cameron insisted he did not duck his responsibilities for "one second".
"I think we need to be absolutely clear that the ministerial code is for me, the behaviour of ministers is for me," he said.
"If ministers have behaved badly, broken the ministerial code, it is my responsibility either to ask Alex Allan's advice about what should happen or to take action myself and say they can't remain in the government."
On Sunday the prime minister said Hunt's special adviser Adam Smith had been right to resign over his contacts with News Corporation lobbyist Frederic Michel, which were "too close, too frequent".
But he added: "I don't think it would be right in every circumstance if a special adviser gets something wrong to automatically sack the minister."
Labour accused Hunt of having misled parliament when he told the Commons last year he was releasing "all the documents relating to all the meetings, all the consultation documents, all the submissions we received, all the exchanges between my department and News Corporation".
Last week a raft of emails between Rupert Murdoch's company and Hunt's office came to light for the first time - exposing the culture secretary to damaging allegations that he supported News Corporation's bid when he was supposed to be impartial.
Labour's deputy leader and shadow culture secretary Harriet Harman said it was "already evident that Jeremy Hunt has breached the ministerial code".
"Not only has he breached the ministerial code in many, many ways, but even more seriously than that when he was responsible for acting quasi-judicially on a hugely important takeover bid of £8 billion he did not act impartially.
"I just think it says everything about David Cameron that he is refusing to refer him to Sir Alex Allan, to investigate all these breaches of the ministerial code."