The UK Government is facing two court battles with green activists over the approval of the Rosebank oil field in the North Sea.
Uplift is claiming the energy secretary failed to show Rosebank aligns with the government's net zero plans, while Greenpeace says the approval process did not consider the pollution that would come from burning oil, and the project would damage the marine wildlife.
The UK Government "strongly rejects these claims".
Both groups have applied to the Court of Session in Edinburgh for a judicial review of the energy secretary's decision and the North Sea Transition Authority's (NSTA) consent to the project.
Tessa Khan, executive director of Uplift, said: "If Rosebank goes ahead, the UK will blow its own plans to stay within safe climate limits. It's that simple.
"If the Government disagrees, it needs to provide evidence and prove it in court. The regulator also needs to be open about its reasons for approving a huge oil field when we're facing a worsening climate crisis."
A government spokesperson said: "The UK is a world leader in reaching net zero - cutting emissions faster than any other major economy - and as the independent Climate Change Committee recognises, we will still need oil and gas as part of our energy mix.
"We will continue to back the UK's oil and gas industry, which underpins our energy security, supports up to 200,000 jobs, and will provide around £50 billion in tax revenue over the next 5 years - helping fund our transition to net zero."
According to an independent socioeconomic report by Wood Mackenzie and Voar Energy, Rosebank is estimated to create £8.1b of total direct investment over the lifetime of the field, of which 78% is likely to be invested in UK-based businesses.
It is expected to support around 1,600 jobs during the height of the construction phase of the project, and it will continue to support around 450 UK-based jobs during the lifetime of the field.