Senior judges were due to hear an appeal against the jail terms handed to three fracking protesters for causing a public nuisance.
Soil scientist Simon Blevins, 26, from Sheffield, and teacher Richard Roberts, 36, of London, were both jailed for 16 months, while piano restorer Rich Loizou, 31, from Devon, was given 15 months.
They climbed on to lorries outside energy firm Cuadrilla's fracking site in Preston New Road, Little Plumpton, Lancashire, in a protest last July which lasted almost 100 hours.
The three activists were jailed in September after being convicted of public nuisance following a trial at Preston Crown Court.
They were due to challenge their sentences before three judges at the Court of Appeal in London today.
Supporters said they will gather outside the court for a "silent demonstration" before the hearing.
At the sentencing on September 26, Judge Robert Altham said he could not suspend the jail terms despite accepting the impact of incarceration and the good they did in the community.
He told Preston Crown Court: "I do find they provide a risk of reoffending.
"Each of them remains motivated by unswerving confidence that they are right. Even at their trial they felt justified by their actions.
"Given the disruption caused in this case, only immediate custody can achieve sufficient punishment."
Blackpool South MP Gordon Marsden has written to the Attorney General over the case with a series of questions after it was revealed that the judge's family had business interests linked to the offshore gas industry.
Mr Marsden asked the Attorney General: "If he will publish the guidance issued by his Department on the duty of care required of justices under the judicial code of conduct when presiding over a case where the circumstances involve industries in which the judge's family members have a financial interest."
He has also asked: "Whether the Judge in the trial at Preston Crown Court in relation to Simon Blevins, Richard Roberts and Richard Loizou sought advice from (a) his Department and (b) the Ministry of Justice on the requirements of the Judicial Code of Conduct in relation to family connections?
He has also asked t if the Attorney General will "undertake an investigation into compliance with the Judicial Code of Conduct in relation to the trial/"
A fourth defendant, Julian Brock, 47, from Torquay, was sentenced to 12 months in custody, suspended for 18 months, after he admitted public nuisance.
Mr Brock is not challenging his sentence.
Last week Cuadrilla was given the go-ahead to start work at the site following a failed High Court bid by campaigners to block fracking due to safety concerns.
The appeal will be heard by Lord Chief Justice Lord Burnett and two other leading judges.