South Cambs Lib Dems, lead by GCP vice-chairman Aidan Van de Weyer, demand that it is taken off the table.
Network Rail says it is hoped it could open by 2025.
87 per cent say living near nature is beneficial during the coronavirus outbreak
The GCP has removed its latest plans from its board agenda to consider the Combined Authority’s alternative.
Cllr Aidan Van de Weyer will take on Conservative James Palmer in next year's elections
It says more detail is needed first on the metro plans and East West Rail.
The Greater Cambridge Partnership and Combined Authority are locked in a furious row over £160.5m scheme.
Combined Authority leader says GCP has listened to views in city - and ignored everyone else, including him.
The Greater Cambridge Partnership has scrapped plans to take C2C busway via Adams Road.
A consultation was launched on Monday into the policies behind the ambitious CAM scheme.
A leading councillors says CAM funding is more unlikely with the UK government facing a huge debt because of the coronavirus.