Insulate Britain has pledged to restart its road-blocking protests despite legal injunctions which mean its members risk being fined or jailed.
Earlier this month the organisation announced it was temporarily suspending its "campaign of civil resistance" which had caused chaos by blocking major roads around London.
But a spokesman said that "there are things happening" that would target morning rush-hour traffic on Monday when the protests resume.
Police have made multiple arrests during the demonstrations, with angry motorists often clashing with protesters.
Several injunctions against the protesters granted by the High Court in recent weeks means anyone breaching the order by blocking roads could face a prison sentence, Transport Secretary Grant Shapps has said.
The Metropolitan Police said it had an appropriate policing plan in place and would respond accordingly to any new protests.
A spokesperson for Insulate Britain said: "I don't know why they have decided to use court injunctions. Injunctions change nothing.
"We will be back to continue until the government give us a meaningful statement that we can trust and then we will be off the roads immediately, other than that the injunctions or the threats of prison don't anything."
The group is calling for the government to insulate all homes in the UK by 2030 to cut carbon emissions.
In the five weeks before announcing the pause on 14 October, the group blocked roads, often by gluing their hands to the carriageway in order to increase the time it took police to remove them.
Responding to the suggestion that the disruptive protests are losing public support, the campaign spokesman said: "It is becoming a binary decision whether people are resisting the facilitation of the destruction of their country, their families, their communities and everything they hold dear or whether they are going to go into resistance against it.
"What we are saying now is that the public need to join us on the roads because the government are basically committing treason," they said.
A spokesperson for the Department for Transport said: "Insulate Britain's actions are dangerous and disruptive, and we urge them to call off their reckless campaign for good.
"National Highways is now taking the first group of activists from Insulate Britain to court, for breaching injunctions by blocking the M25.
"We will continue working with the police to bring those who carried out dangerous and disruptive action to justice. Those activists will now receive a court summons and could face imprisonment and/or an unlimited fine.
"Timings are now in the hands of the court but we expect hearings will take place as soon as possible."
Insulate Britain previously admitted its actions on the M25 were "in breach" of an injunction obtained by the government last month.
People who break injunctions can be found to be in contempt of court, but the protests continued as prosecutions usually take several months.