Labour MPs have called on the government to reject the Rosebank oil field, saying it is "incompatible" with the UK's climate commitments.
There is a growing expectation among senior Labour figures that drilling in the oil field off the north-west coast of Shetland will be given the go-ahead.
Prime Minister Andy Burnham said on Wednesday that a decision would be "taken in due course" while Energy Secretary Miatta Fahnbulleh stressed that affordability of energy bills was her "overriding objective".
But in a sign of the division within the party, about a dozen Labour MPs expressed concerns about approving it during a Westminster Hall debate in Parliament.
Separately, it is understood some Labour backbenchers have organised a letter opposing Rosebank - intended for Burnham, but not yet sent - which more than 60 out of about 400 Labour MPs have indicated they support.
One signatory told the BBC that approving Rosebank "would not create new jobs, would bring minimal money into the Treasury and be bad for the climate".
"The government's central aim is to tackle the cost of living crisis, and drilling for more oil at Rosebank isn't the answer," the MP said.
Wednesday's Westminster Hall - a type of parliamentary debate where backbench MPs raise topical issues but do not vote - was organised by Green MP Carla Denyer.
