The High Court will today hear arguments over whether or not to grant a last-minute injunction stopping next week's planned first flight of asylum seekers to Rwanda.
Two campaign groups - Detention Action and Care4Calais - are joining the PCS Union and four individual asylum seekers to bring the legal action.
The Home Office has announced that the first asylum seekers will be sent to Rwanda on Tuesday as part of its new immigration policy.
Lawyers for the groups taking the action will argue the policy puts people's lives at risk and is an unlawful way to treat asylum seekers prior to deportation and once sent to Rwanda.
The groups taking the action have asked that if a ruling goes in their favour the plane is halted completely - so the ruling doesn't only apply to the asylum seekers they are representing.
Sky News is aware of other asylum seekers who have been given removal notices who aren't part of these proceedings.
With just a few days to go until the flight, it's expected a decision could be handed down on the same day as the hearing.
Care4Calais says it's aware of round nine Afghans; 35 Sudanese; 18 Syrians; 14 Iranians; 11 Egyptians as well as Iraqi, Pakistani, Albanian Algerian, Chadian, Eritrean, Turkish and Vietnamese people who have been told they could be put on the first flight.
'We hope the courts will agree with us'
Clare Moseley, founder of Care4Calais, said: "We have spoken to nearly 100 people in detention who've been told they will be forcibly sent to Rwanda. Almost all are overwhelmed by total shock and despair.
"Many came to the UK believing it to be a good place that would treat them more fairly than the places from which they escaped. We say that the Rwanda plan is unlawful. We hope the courts will agree with us."
Efforts to secure an injunction are an eleventh-hour attempt by campaigners to stop the flight.
Care4Calais, Detention Action and the PCS union have already issued judicial review proceedings and want the lawfulness of the policy tested in court.
The Home Office says it wants to stop the trade of people smugglers transporting people across the channel and sending asylum seekers to Rwanda is part of efforts to "overhaul" the UK's "broken" system.
The government says it's committed to working with Rwanda to offer safety to those seeking asylum and those recognised as refugees will be given an opportunity to rebuild their lives.
Anyone the Home Office considers has taken a dangerous, unnecessary or illegal journey to the UK would meet the criteria for removal apart from lone migrant children who are exempt.
The prime minister's official spokesman said: "We remain confident in our position. Should the legal challenges require us going to the courts we will argue the case.
"It's true to say the first flight is due for next week so we have that ready to go."