Environmental charities have formed an alliance calling on the government to reconsider its approach to a London-to-Birmingham high-speed rail line.
The new grouping, including the Campaign to Protect Rural England, RSPB and Greenpeace, says there has been too little consultation on the HS2 scheme.
It fears there will be increased flights or car journeys if the proposals fall through.
The government says it is already acting on the charities' concerns.
The charter sets out four principles "for doing High Speed Rail well".
It is also backed by Campaign for Better Transport, Chiltern Society, Civic Voice, Environmental Law Foundation, Friends of the Earth, The Wildlife Trusts, and Woodland Trust.
It calls for a national transport strategy; better long-term planning of the effects of big transport proposals; and effective public participation.
The alliance says: "Many groups commenting publicly on High Speed Rail to date have represented either people living along the proposed route or businesses and cities that could profit from it.
"Today's Charter draws together for the first time many well known national charities, covering environmental, heritage, countryside, legal and wildlife issues, in addition to other organisations. It seeks to achieve the best long-term outcome from high speed rail for the country, the climate, communities and the countryside."
They say HS2 has been foisted on the public with no prior consultation.
Ralph Smyth, of the Campaign to Protect Rural England (CPRE), said slower trains would help because it would make more routes available for consideration and provide more opportunities for engagement with local communities.
"If they keep to a 250mph design speed it has got to be a straight railway," he said.
HS2 is designed to shorten journey times between London and Birmingham, and connect later to Manchester and Leeds.
A public consultation on the proposed location of the new track in the Chilterns, Buckinghamshire and Warwickshire is running until July, but some residents have already voiced concerns about the impact.
If the plans go ahead, the government expects work on the line to the West Midlands to begin in 2015 and finish by 2026, with the links to Manchester and Leeds completed in 2032-33.
Earlier this month a group of 21 business figures and politicians called for the proposed link between London and Birmingham to be scrapped.
In the open letter signed by the likes of former Chancellor, Lord Lawson, and Lord Wolfson, the chief executive of Next, the plan was described as an "expensive white elephant", and a "vanity project".
But in February, another 69 business leaders wrote a letter to the Financial Times in support of the plans.
Transport Secretary Philip Hammond said the £17bn project will deliver major strategic benefits to the economy: "I am pleased that so many respected organisations are voicing their support for high speed rail and they should be assured that the government is already acting on their points of concern.
"The government has a clear strategy for a greener, more efficient and more productive transport system with high speed rail at its heart.
"That strategy includes investment in our existing roads and railways, promoting the use of electric cars and other forms of sustainable transport as well as tackling congestion and promoting more sustainable aviation."