Justine Greening must pledge her support to preventing cuts to the foreign aid budget in the wake of reports she does not support the work of her new department, the Labour Party has said.
On Friday The Times (£) reported that Greening was "not very happy" with the decision to move her from the transport department to the Department for International Development.
According to the paper Greening "questioned the work of the department and its budget" during her meeting with the prime minister.
While the Daily Telegraph's Ben Brogan reports that Greening used "rather earthy terms to say that working with foreigners wasn't her political ambition".
Labour's shadow development secretary Ivan Lewis wrote to Greening last night asking her to "allay concerns" that she would not protect her department's budget.
The letter also asked her to "reiterate the government’s continued support for Mark Hendrick’s Private Members’ Bill when it returns to the House of Commons".
"This would deliver on your manifesto commitment and the coalition agreement to enshrine 0.7% in law," Lewis said.
Part of David Cameron's plan to "de-toxify" the Tory brand was his pledge to meet the goal of spending 0.7% of GDP on development aid by ring fencing the DfID budget.
The decision to spend large amounts of money on foreign aid at a time that budgets are cut at home has proved controversial, especially with many Tory backbenchers.
Greening's predecessor, Andrew Mitchell, was vocally supportive of the aid target, and Labour is concerned that Greening will be more sympathetic to backbench complaints.
In July Peter Bone infuriated development minister Alan Duncan by blocking an attempt to enshrine the 0.7% target in law.
Bone torpedoed the move by talking out the Hendrick's Bill, causing a furios Duncan to slam his hands down on the government front bench after Big Ben tolled 2.30pm and the Bill's time expired.
Defending the policy in August, Cameron said: "I think most people recognise that when there are 170 million people around the world suffering from malnutrition, when there are millions of people living on less than a dollar a day, even at a tough time in Britain, we are right to meet our aid commitments."
Greening is believed to have been shuffled out of her job at the transport department in order to pave the way for a U-turn on the expansion of Heathrow.
The new development secretary led the opposition to the construction of a third runway at the airport as it would increase noise pollution over her West London Putney constituency.