The UK government has said rules allowing EU nationals to live and work freely in the UK will end in the event of a no-deal Brexit on 31 October.
Theresa May had considered extending freedom of movement to 2021 or allowing EU citizens to stay for three months before applying for a longer stay.
Those options have now been dropped, in favour of a new approach to be set out later.
Boris Johnson said the UK would not “become hostile to immigration”.
The PM added that “immigration into the UK will be democratically controlled”.
The Three Million group, which campaigns for the rights of EU citizens living in the UK said: “Ending freedom of movement without putting legal provisions in place for those EU citizens who have not yet successfully applied through the settlement scheme will mean that millions of lawful citizens will have their legal status removed overnight.”
Freedom of movement allows EU citizens to live and work in other European Union countries.
In a statement, the Home Office said: “EU citizens and their families still have until at least December 2020 to apply to the EU Settlement Scheme and one million people have already been granted status.
“Freedom of movement as it currently stands will end on 31 October when the UK leaves the EU, and after Brexit the government will introduce a new, fairer immigration system that prioritises skills and what people can contribute to the UK, rather than where they come from.”
A Downing Street spokeswoman added that “tougher criminality rules” for those coming to the UK will be introduced.
Under the withdrawal agreement, negotiated by former Prime Minister Mrs May with the EU, freedom of movement would have stayed for a two year transition period.
However MPs repeatedly voted down Mrs May’s deal and unless an agreement can be reached the UK will leave without a deal on 31 October.
In a no-deal scenario, those EU citizens with the right to permanent residence in the UK – which is granted after they have lived in the UK for five years – should not see their rights affected.
EU nationals who are already in the UK would be unaffected and can apply for settled status or pre-settled status in the same way as now.
The changes to freedom of movement will not affect Irish citizens. In May, British and Irish ministers signed a deal to guarantee free movement for their citizens crossing the Irish border and cross-border access for study and health care.
‘Irresponsible and reckless’
The Lib Dems’ home affairs spokesperson Sir Ed Davey accused the government of being “irresponsible and reckless”.
He said “employers up and down the country won’t know what the law is”, adding “this will hugely increase the damage cause by a no-deal Brexit”.
Director of the Migration Observatory, Madeleine Sumption, said ending freedom of movement could “simply mean ending the role of EU law in governing the rights of EU citizens here and replacing it with UK law”.
However, she said it could also mean introducing a new “substantially more restrictive” system.
She said it would be “quite difficult” to enforce any new rules before the process of registering those EU citizens who have already been living in the UK for years has been completed.
BBC home affairs correspondent Danny Shaw said the logistics of the new scheme still had to be worked out.
“You’ve got to remember this: 40 million people arrive from the EU, EU nationals, every year into the UK. So for the ports and airports that will mean enhanced checks if freedom of movement rules are abolished straightaway and that will put quite a burden on the staff working at Britain’s ports and airports.”