The activists, from climate change campaign group Plane Stupid, will be supported by a demonstration outside Uxbridge Magistrates Court on Tuesday (April 19) ahead of the hearing.
The self-proclaimed 'Heathrow Tunnel Trio' - Esme Waldron, 23, and Alistair Cannell, 26, both from Brighton, and William Pettifer, 27, from Radford, Somerset - are expected to plead guilty and be sentenced for blockading the entrance tunnel to Heathrow Terminals 1, 2 and 3 on November 26 last year.
They will be joined at Uxbridge Magistrates' Court by supporters including many of the Heathrow 13, who were given suspended jail sentences for blockading the runway at Heathrow in February.
They are represented by Mike Schwarz from Bindmans solicitors. Supporters are expected to gather outside the court at 9am. They will include local residents and environmental activists.
The trio previously denied unlawfully blocking a tunnel, contrary to the Heathrow bylaws, at Uxbridge Magistrates Court on Wednesday December 23.
The protest in question took place on November 26, when demonstrators from Plane Stupid parked a vehicle across both lanes of Heathrow's main entrance tunnel during the morning rush hour .
'No ifs, no buts, no third runway'
A total of five people were arrested in connection with the demonstration, with the other two bailed to return to a west London police station pending further enquiries.
Waldron said: "For most of us, all we'll gain from new runways is dirtier air, noise and more floods due to climate chaos.
“There are more than enough runways for people who take one holiday a year. Demand for airport expansion only comes from a minority of frequent leisure flyers.
“This 15% of British people take 70% of our flights, often to second homes abroad and they have a high income”.
Waldron, 23, believes the matter is a “class issue” and is a familiar story of rich and powerful elite trampling over the livelihoods of those lacking power.
She added: “While the huge business entity that is Heathrow spends tens of millions advertising its plans for expansion, where are the voices of the locals whose lives will be entirely uprooted or the climate refugees who are forced to migrate as global warming increases drought?”
Edward Thacker is one of the Heathrow 13 who moved to Sipson to oppose the construction of a third runway at Heathrow.
He said: "Giving us suspended jail sentences will not stop protests against new runways.
“If the government gives the green light to a new runway, it is likely to result in one of the largest campaigns of environmental civil disobedience since the anti-roads movement of the nineties."
John Stewart, chair of the residents’ organisation HACAN, said, “Last time round direct action played an important part in defeating a third runway.
“The government ignores these protests at its peril.”