Campaigners against the HS2 rail scheme have confirmed they will make two court bids to halt the £33bn project.
The HS2 Action Alliance is seeking two judicial reviews into the government's handling of the plan, to link London and Birmingham by rail in 45 minutes.
It claims ministers failed both to carry out environmental assessments and to consult properly over compensation.
The government has said it "struck the right balance" between people's concerns and the national interest.
HS2 won ministerial approval in January, despite strong opposition, with Transport Minister Justine Greening saying the 14 trains per hour in each direction would create "jobs, growth and prosperity".
Its first phase, reducing the London-Birmingham journey time from one hour 24 minutes, is intended to be operational by 2025, with consultation on extensions to Manchester and Leeds to begin in 2014.
However, the action alliance - which has the backing of more than 70 opposition groups - claims the government failed to follow the proper processes in approving the scheme, much of which goes through Buckinghamshire and Northamptonshire.
On the environment, which will be the subject of one of the legal battles, it says the government failed to carry out a full strategic assessment of the project's impact ahead of consultation.
The other action will contend that "inadequate information was provided in the consultation, preventing the public from being able to give a meaningful response".
"The decision was without proper justification, ignored their own criteria and relied on new undisclosed material," the group claims.
HS2 Action Alliance said on its website there had been a "brilliant response" from the public to its appeals for funds to raise the six-figure fee needed for legal action.
"We have two strong legal teams who are specialists in their fields and believe we have two powerful cases that the government must now answer," it said.
The government has 21 days to respond before a judge will decide whether the challenges will be allowed.
Previously, the Department for Transport said the route had been continually improved to mitigate the impact both on those living near it and the environment.
"We believe we have struck the right balance between the reasonable concerns of people living on or near the line - who will be offered a package of compensation measures - the environment and the need to keep Britain moving," a spokesman said.
Last week, another anti-HS2 coalition launched a similar legal action.
The 51m Group - made up of 15 local authorities - is challenging the rail link on a range of grounds including the allegation that the government failed to consult properly on the original route, or the revised version of which was announced in January.