EU citizens living in the UK are in Brussels to urge members of the European Parliament and Commission to ensure their rights are guaranteed after Brexit.
Anne-Laure Donskoy will tell MEPs that EU citizens' rights "to work, to marry, to have access to health services and education, to build a business" are "at risk" and should be "guaranteed and preserved not just for the short or medium term but permanently".
Ms Donskoy, co-chair of the 3 million group, a grassroots organisation formed after the Brexit referendum to campaign for the rights of EU citizens in the UK, is addressing MEPs, including the Parliament's Brexit coordinator Guy Verhofstadt.
Members of the 3 million will also meet representatives from the other 27 member states.
They are demanding an "early, legally binding and separate agreement" on citizens' rights, registration and voting rights.
The future of around three million EU residents in the UK and one million Britons in the 27 member states has been uncertain since June 23, when Britain voted to leave the EU.
In March, MPs overturned a House of Lords amendment to the Article 50 bill which would have protected the rights of the EU citizens in the UK.
Theresa May has said any agreement must include the rights of Britons living in the EU.