Campaigners from Stop HS2 have slammed bosses of the influential business lobby group, accusing them of "losing all credibility" after failing to acknowledge any downsides to the line.
The CBI has hit back, saying the group was a modern day "flat earth society" and insisting there was clear evidence that HS2 would benefit the country.
It comes after a joint statement from six CBI regional councils called on the Government to be "bold" and deliver the line in its entirety.
HS2 is currently under review, with its future plunged into doubt over concerns that it will bust its £55 million budget and take years longer to complete than planned.
Joe Rukin from the Stop HS2 group, said: "In calling for the Government to scrap the long overdue scrutiny of this project, the CBI have lost all credibility.
"It is exactly this sort of 'let's just get on with it, no matter what the cost' attitude which has led to the complete mismanagement of the project, the rampant cost escalation, the abandonment of all original timescales and a complete lack of support from the general public.
"Yet again an organisation which is acting as a mouthpiece from the vested interest construction sector who intend to cash in billions from building HS2 has simply invented illusionary benefits in an act of desperation to stop this project being cancelled."
Penny Gaines, Chair of Stop HS2, said: "In the last two months it has been revealed that HS2 is vastly over-budget and massively behind schedule and yet the CBI are refusing to acknowledge that there are any downsides to the project.
"Part of the review was to look at alternatives to the existing program schedule for HS2, and this have been dismissed out of hand by the vested interest lobbyists at the CBI.
"With a price tag of £80 billion and rising, HS2 is simply the wrong project for the country."
In response CBI regional director Richard Butler, said: “Obviously a small group of people have valid concerns and that is why the planning process exists, to make sure everything is done – fairly and correctly.
“But the Stop HS2 group are another matter entirely, they just go around throwing accusations that untrue and wrong.
"They are the modern political equivalent of the flat earth society, trying to stop economic progress and job creation in our region.
"I’m sure in another era they would have opposed the trains or even the canals like they do now with HS2.
“All the evidence is clear, HS2 will create jobs, investment and regeneration opportunities for places like the Black Country and the CBI wholeheartedly support it.”