Hillingdon Council and HS2 Action Alliance will appeal the High Court ruling dismissing the latest challenge to the Government over HS2.
Ray Puddifoot, the leader of Hillingdon Council, which brought the action along with HS2 Action Alliance, said: "It's a disappointment and we are considering appealing."
He said intention to appeal had been lodged with the court today (Wednesday, August 6) after the decision was handed down by Mr Justice Lindblom, and the two parties would be getting together to discuss the matter soon.
Mr Puddifoot said: "Our barrister said we had an extremely good case, and [the ruling] just flew in the face of what we would think justice to be."
He went on: "It seems we get some very strange decisions from judges when it comes to European law."
Keri Brennan of Hillingdon Against HS2 (HAHS2) said: "I think, as always, there was a good argument there, and we are just gutted.
"I'm not surprised but I am disappointed."
Mrs Brennan went on to say that the battle to stop HS2 was far from over and added: "There is so much still to play for."
Doreen McIntyre of Harefield Against HS2 said the ruling "doesn't change anything about the HS2 proposal, the toll it is already taking on communities like Harefield or the devastating impact it would have if built.
"It might not be technically unlawful but that doesn't make it right. In Harefield, we are carrying on quietly getting ready to spell out the impacts one by one through the petitioning process. The fight is uninterrupted as far as we are concerned," she said.
