They say these range from disability and family rights to data protection and employment rights and the right to a fair trial.
The concerns were aired at a conference that was co-hosted by New Europeans, a group that campaigns for citizens’ rights after Brexit.
The fears about human rights come with exactly one year to go before the UK leaves the EU.
The event, in London, was organised to look at the possible impact leaving the European Union will have on human rights.
Others involved were the European Association for the Defence of Human Rights (AEDH), Britain in Europe and Brunel University’s Knowing Our Rights.
Among the speakers was Roger Casale, CEO and founder of New Europeans, who said he wanted to highlight the “importance of reframing Brexit as a human rights issue.”
He said, “The referendum has stripped rights from everyone - UK and EU citizens alike. New Europeans have been clear from the start that we should not be negotiating EU citizens’ rights and the need for immediate comprehensive unilateral guarantees of EU citizens’ rights.
“As such, we have been campaigning for a ‘Green Card for Europe’ to protect these fundamental rights.”
He said, “the prolonged anxiety felt by hundreds of thousands of families whose lives are in limbo” may lead to Article 8 claims against the UK at the European Court of Human Rights.
The European Court of Justice may be asked to decide whether British citizens in the EU “can be stripped of any of their EU citizenship rights at all.”
Geoffrey Nice, from Britain in Europe, said, “It is imperative that we take a stand and ensure that fundamental human rights are not just on paper but implemented and protected.”
Meanwhile, Jonathan Portes, of King’s College London and a senior fellow of the UK in a Changing Europe programme, says that free movement “has been good for the UK - and when it ends, there will be consequences.”
Commenting on the interim report by the UK’s migration advisory committee, he said, “Employers are very worried about the potential impact of ending free movement. This perhaps is no surprise.
“But it’s worth noting that this extends across a wide range of sectors and ranges far beyond the stereotype of EU migrants filling low-skilled, low-paid jobs.
“Migration from Europe fell sharply after the Brexit vote - even though nothing has changed yet. As the consequences for employers and public services become increasingly apparent, politicians should remember that immigration may be just as big a problem when it is falling as when it is rising.”