Proposals in the plan include the construction of 23,000 homes each year and clusters of tall buildings in areas such as the Isle of Dogs and Paddington.
A partnership source said: "The general view is that there is a need for a vision for London. The big concern is deliverability; it's all very well all this property being talked about, but what about the deliverability of the infrastructure?"
The group's concerns will be put to a party of authority representatives at the end of next week. These are expected to include deputy mayor Nicky Gavron and authority head of planning and strategy Greg Clarke.
A preliminary meeting was held by the members last week to decide which issues should to be brought up with the authority. The consensus was that the plan's targets were unachievable. A source said: "Someone asked if anyone thought that CrossRail could be delivered by 2011, and nobody said yes." CrossRail is intended to link the Isle of Dogs in east London with central London.
The meeting with the GLA will be chaired by Ken Dytor, chairman of developer Urban Catalyst. Dytor declined to comment.
The draft London Plan was unveiled last month and is to go out for a three-month consultation. A final version is expected to be publish next year.
The plan has already been criticised by the House Builders' Federation for putting pressure on developers to include 50% affordable housing in new developments. The HBF believes that 20-25% is a more realistic target.
Livingstone has demanded an extra £150m a year from the Housing Corporation to help achieve its housebuilding aims. This additional funding is yet to be secured, although the authority already gained an initial grant increase of £102m earlier in the year.