Charities supporting asylum seekers plan to launch legal challenges "as quickly as possible" against moving people to Rwanda, after a new law passes in the coming days.
Legislation to declare Rwanda safe is likely to pass its final parliamentary hurdles this week.
Downing Street hopes this will allow the first flights to take off before the end of spring.
Ministers hope to strike similar removal deals with other countries.
But Charity Care4Calais - which helped block flights to Rwanda last year - said it had recruited hundreds of volunteers to identify people who are set to be removed to the east-central African country.
It intends to offer them legal support to try and keep them in the UK.
A source said: "Human rights still apply - we are ready to go".
The government is eager to remove some asylum seekers to Rwanda before the general election, as part of its strategy to stop small boats crossing the English Channel.
The legislation, which will pass Parliament soon, declares Rwanda a safe country - after the Supreme Court blocked an earlier plan in November.
The Rwanda scheme was originally introduced by Boris Johnson in April 2022.
It has faced a number of legal challenges since, and so far no asylum seekers have been sent to the African country.
But there is increasing confidence from the government that they can now get the plan off the ground.
Legal battles coming
There has been intense debate in Parliament, with the Lords making several changes to the government's bill.
But that process - known as ping-pong - is widely expected to have concluded by Thursday this week.
The Home Office can then begin informing people who are to due to be removed to Rwanda. It is at that stage that charities intend to begin legal challenges, which could delay removals.
It is also possible the entire premise of the legislation will be challenged in the courts too.
As well as legal battles, it is certain the political debate will continue.
Ministers say sending some asylum seekers to Rwanda will help deter people from making crossings across the Channel on small boats.
Government sources say other countries will follow suit, if the UK scheme is successful.
They also believe other countries will be willing to take asylum seekers from the UK if the Rwanda partnership is seen to work.
Heated political debate
But Labour has said it will scrap the scheme if it wins power. The party believes it is too expensive, and unworkable.
Instead, it wants to work more closely with Europe, take firmer action on smuggler gangs and invest in clearing the UK's backlog in asylum applications.
But expect a heated political debate in the coming days.
A source close to Home Secretary James Cleverly said: "Labour - who have tried everything to disrupt, delay or destroy the bill - are increasingly worried it will work.
"We know a deterrent is needed, and we know deterrence works from the evidence of our deal with Albania. We also know Labour don't have one."
Labour says that is nonsense.
Sources acknowledge some flights to Rwanda are likely to take off, but say the challenge will be whether enough people are removed to have an impact.
They also point out that the government has already passed two significant pieces of legislation on small boats - only for the numbers to remain high.
The number of people crossing the Channel on small boats fell last year, from a record high in 2022. But it remained the second highest on record, at 29,347.
Home Office figures also suggest a record number of people crossed the Channel in the first three months of this year, when compared to the same period in previous years.
That makes it a key test for the government - and a key political debate.
