Environment secretary Hilary Benn has appeared to express doubts over the expansion of Heathrow airport.
In an interview with the Sunday Times, the cabinet member said he was concerned that the UK would breach its obligations on pollution control measures if the building of the third runway went ahead.
Speaking to the paper, Mr Benn said a public consultation revealed that there were concerns about the noise caused by the larger airport as well as the impact on air quality.
Commenting on the consequences of not meeting pollution targets, he said: "You are then in trouble with the commission, you get infraction proceedings and then off you go - which is not something we can contemplate.
"We have to achieve the environmental objectives. We have to honour that commitment and I am determined that we will," he added.
Previously, the government has committed itself to building the third runway but transport secretary Geoff Hoon delayed a final decision on the matter until January.
The Sunday Times has seen Mr Benn's comments as a "cabinet split" and stated that he did not express support for the project during the interview. It also reports that other cabinet members such as the energy and climate change secretary Ed Miliband, the foreign secretary David Miliband and Commons leader Harriet Harman secretary have expressed doubts over the project.