Up to a hundred EU nationals living in Britain have been mistakenly sent letters from the Home Office threatening them with deportation.
The mistake emerged after Finnish academic Eva Johanna Holmberg, who has the right to live in the UK, received a letter telling her she had a month to leave.
A Home Office spokesperson said the letters had been sent out in error and the matter was being urgently investigated.
"The rights of EU nationals living in the UK remain unchanged," the spokesperson said. Everyone who received a letter would be contacted to "clarify that they can disregard it".
But critics said it demonstrated the government's incompetence over immigration and citizens' rights.
James McGrory, executive director of pro-Remain group Open Britain, said: “It’s little wonder that many EU citizens feel worried about their future status in the UK when they hear of people with every right to be here getting letters threatening their deportation.
“The Home Office show scant sign of being able to get a completely new immigration regime up and running by 2019. Ministers should drop their damaging rhetoric about an immigration target and instead come forward with proposals that recognise the work of EU nationals already in this country, and others who we will undoubtedly need in the future.”
Liberal Democrat shadow home secretary Ed Davey added: “These letters shame Britain. EU nationals who have made their lives here are already facing huge uncertainty over Brexit.
“This catastrophic error is a sign of the chaos and incompetence at the heart of this Conservative government."