Rural Conservative councillors are taking on the government's flagship High Speed 2 rail project with a week of legal challenges.
The route cuts through rural Conservative heartlands in Buckinghamshire and Warwickshire as well as the Chilterns, a designated area of outstanding natural beauty.
The group, called 51m, is challenging the legitimacy of a consultation carried out between February and July last year which preceded the government's decision to press ahead.
"When you have Conservative councillors bringing a case against Conservative ministers in a Conservative-led government, you know that we are very confident that there are huge flaws in the HS2 project," said StopHS2 campaign manager Joe Ruskin.
"We have an extremely strong case against HS2 and it is time that the government looked at the facts and cancelled HS2 immediately."
Campaigners believe the consultation did not fully take into consideration the impact on communities or the environmental cost of the work. They claim some information provided to the consultation was inaccurate.
Over the weekend it emerged that the top speed of trains running on HS2 might be cut from 400 to 300kph, a key criticism by environmental campaigners. It is expected that journeys from London to Birmingham will still be reduced to under an hour.
Opponents have argued that the reduced journey times do not justify the projected £33 billion cost of building the new rout, which will eventually go on up to Leeds.
The Department of Transport said earlier they were expecting a victory in the case.
"While it would not be appropriate to comment on the specific claims, the government is confident that the decisions on HS2 have been taken lawfully and fairly and it is vigorously defending these legal challenges," a spokesperson said.
Construction is not due to start for another five years and phase one (from London to Birmingham) is not expected to start taking passengers until 2026.